Functionalneuroanatomyofmeditation · Functionalneuroanatomyofmeditation...

Functional*neuroanatomy*of*meditation*

MANUSCRIPT+IN+PRESS+AT+NEUROSCIENCE)AND)BIOBEHAVIORAL)REVIEWS) 1*

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Functional+neuroanatomy+of+meditation:+A+review+and+meta?analysis+of+78+functional+

neuroimaging+investigations+

Kieran*C.*R.*Foxa,*,*Matthew*L.*Dixona,*Savannah*Nijeboera,*Manesh*Girna,*James*L.*Flomanb,*

Michael*Lifshitzc,*Melissa*Ellamild,*Peter*Sedlmeiere,*and*Kalina*Christoffa,f*

*

a*Department*of*Psychology,*University*of*British*Columbia,*2136*West*Mall,*Vancouver,*

B.C.,*V6T*1Z4*Canada*

b*Department*of*Educational*and*Counselling*Psychology,*and*Special*Education,*University*

of*British*Columbia,*2125*Main*Mall,*Vancouver,*B.C.,*V6T*1Z4*

c*Integrated*Program*in*Neuroscience,*McGill*University,*3775*University*St.,*Montreal,*QC,*

H3A*2B4*

d*Neuroanatomy*and*Connectivity*Research*Group,*Max*Planck*Institute*for*Human*

Cognitive*and*Brain*Sciences,*Stephanstrasse*1a,*Leipzig,*Germany*04103.*

e*Institut*für*Psychologie,*Technische*Universität*Chemnitz,*43*Wilhelm_Raabe*Street,*

Chemnitz,*Germany*

f*Brain*Research*Centre,*University*of*British*Columbia,*2211*Wesbrook*Mall,*Vancouver,*

B.C.,*V6T*2B5*Canada*

**To*whom*correspondence*may*be*addressed*(at*address*a*above).*Telephone:*1_778_968_

3334;*Fax:*1_604_822_6923;*E_mail:*[email protected]*

*

*



Abstract+

Meditation*is*a*family*of*mental*practices*that*encompasses*a*wide*array*of*

techniques*employing*distinctive*mental*strategies.*We*systematically*reviewed*78*

functional*neuroimaging*(fMRI*and*PET)*studies*of*meditation,*and*used*activation*

likelihood*estimation*to*meta_analyze*257*peak*foci*from*31*experiments*involving*527*

participants.*We*found*reliably*dissociable*patterns*of*brain*activation*and*deactivation*for*

four*common*styles*of*meditation*(focused*attention,*mantra*recitation,*open*monitoring,*

and*compassion/loving_kindness),*and*suggestive*differences*for*three*others*

(visualization,*sense_withdrawal,*and*non_dual*awareness*practices).*Overall,*dissociable*

activation*patterns*are*congruent*with*the*psychological*and*behavioral*aims*of*each*

practice.*Some*brain*areas*are*recruited*consistently*across*multiple*techniques*–*

including*insula,*pre/supplementary*motor*cortices,*dorsal*anterior*cingulate*cortex,*and*

frontopolar*cortex*–*but*convergence*is*the*exception*rather*than*the*rule.*A*preliminary*

effect_size*meta_analysis*found*medium*effects*for*both*activations*(d*=*.59)*and*

deactivations*(d*=*_.74),*suggesting*potential*practical*significance.+Our*meta_analysis*

supports*the*neurophysiological*dissociability*of*meditation*practices,*but*also*raises*many*

methodological*concerns*and*suggests*avenues*for*future*research.+

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Keywords:+meditation;*open*monitoring;*focused*attention;*functional*magnetic*resonance*

imaging;*meta_analysis;*activation*likelihood*estimation+



1.+Introduction++

Meditation*has*been*used*as*a*tool*to*train*the*mind*for*thousands*of*years*

(Anālayo,*2003,*Iyengar,*2005).*Broadly*speaking,*meditation*practices*involve*the*

monitoring*and*regulation*of*attention*and*emotion*(Lutz*et*al.,*2008b,*Tang*et*al.,*2015).*

Meditation*can*be*either*directed*outward*to*particular*objects*and*sensory*stimuli*or*

turned*inward*to*the*workings*of*the*mind*and*felt*experiences*of*the*body.*A*common*

principle*across*all*forms*of*meditation*is*that*through*specific*and*regular*practice,*the*

ability*to*monitor*and*regulate*mental_physical*processes*can*be*progressively*developed*–*

the*way*performance*on*any*other*cognitive*or*motor*skill*can*be*improved*with*practice*

(Ericsson*et*al.,*1993,*Slagter*et*al.,*2011,*Vago,*2014).*Interest*in*the*neural*basis*of*

meditative*practices*has*increased*enormously*over*the*past*decade,*and*mounting*

empirical*evidence*suggests*that*meditation*indeed*leads*to*or*is*associated*with*

significant*changes*in*cognitive*and*affective*processing*(Sedlmeier*et*al.,*2012),*as*well*as*

alterations*in*brain*structure*(Fox*et*al.,*2014)*and*function*(Cahn*and*Polich,*2006).**

Although*meditative*practices*now*garner*serious*interest*from*the*cognitive*

neuroscience*community*(Fig.*1),*meditation*still*tends*to*be*viewed*as*a*somewhat*

uniform*practice*(e.g.,*(Sperduti*et*al.,*2012).*The*umbrella_term*‘meditation’*encompasses*

a*wide*variety*of*distinct*practices*with*specific*goals*and*methods,*however.*The*varying*

methods*and*scope*of*particular*forms*of*meditation*include*focalizing*and*sustaining*

attention*(Wallace,*2006),*generating*and*maintaining*complex*visual*imagery*

(Kozhevnikov*et*al.,*2009),*improving*emotion*regulation*and*well_being*(Chambers*et*al.,*

2009,*Sedlmeier*et*al.,*2012),*and*deepening*compassion*for*others*(Galante*et*al.,*2014).*



Despite*the*diversity*of*meditation*practices,*few*behavioral,*clinical,*or*

neuroimaging*studies*have*directly*compared*meditation*styles*within*or!across*studies.*

As*such,*little*is*known*about*whether*functional*neural*differences*underlie*each*type*of*

practice*(although*see*(Lou*et*al.,*1999,*Manna*et*al.,*2010,*Brewer*et*al.,*2011,*Lee*et*al.,*

2012,*Tomasino*et*al.,*2013).*Although*mounting*empirical*evidence*suggests*that*these*

distinctive*psychological*practices*may*be*dissociable*at*the*neurophysiological*level*(Lutz*

et*al.,*2008b,*Travis*and*Shear,*2010a,*Josipovic*et*al.,*2011,*Tomasino*et*al.,*2013),*no*

comprehensive*overview*has*adequately*addressed*this*complex*issue.*We*therefore*

attempted*to*synthesize*the*large*and*rapidly*expanding*(Fig.*1)*body*of*work*on*the*

functional*neuroanatomy*of*meditation*practices*in*the*present*review*and*meta_analysis.**

Our*central*hypothesis*was*a*simple*one:*meditation*practices*distinct*at*the*

psychological*level*(Ψ)*may*be*accompanied*by*dissociable*activation*patterns*at*the*

neurophysiological*level*(Φ).*Such*a*model*describes*a*‘one_to_many’*isomorphism*

between*mind*and*brain:*a*particular*psychological*state*or*process*is*expected*to*have*

many*neurophysiological*correlates*from*which,*ideally,*a*consistent*pattern*can*be*

discerned*(Cacioppo*and*Tassinary,*1990).**

Supporting*or*disconfirming*this*prediction*through*empirical*synthesis*is*

challenging,*however,*because*at*present*there*are*few*(if*any)*‘objective’*third_person*

measures*that*can*confirm*engagement*in*a*particular*subjective*state*or*mental*practice*

(Lutz*and*Thompson,*2003,*Fazelpour*and*Thompson,*2015).*Current*investigations*

therefore*necessarily*rely*on*first_person*reports*that*a*specific*mental*practice*is*indeed*

being*carried*out*as*instructed*or*intended.*Acknowledging*this*difficulty,*we*reasoned*that*

if*meditation*practitioners*are*really*engaging*in*the*practices*they*report*to*be*–*and*if*



these*practices*engender*their*intended*effects*and*mental*states*–*then*distinctive*

patterns*of*brain*activation*and*deactivation*should*accompany*each*technique.**

In*line*with*our*hypothesis,*it*has*been*argued*that*various*categories*of*meditation*

are*characterized*by*differential*electroencephalography*(EEG)*signatures*(Travis*and*

Shear,*2010a),*cognitive_emotional*effects*(Sedlmeier*et*al.,*2012),*and*potentially*

neuroanatomical*alterations*(Fox*et*al.,*2014).*In*the*present*synthesis,*we*sought*to*build*

on*prior*reviews*and*meta_analyses*by*examining*the*possibility*that*comparable*

dissociations*might*exist*with*modalities*that*measure*cerebral*blood*flow*(positron*

emission*tomography;*PET)*or*blood_oxygenation*level*(functional*magnetic*resonance*

imaging;*fMRI).*Other*modalities,*such*as*EEG,*have*extremely*high*temporal*resolution*but*

very*poor*spatial*resolution*(or*vice*versa,*in*morphometric*neuroimaging).*Functional*

neuroimaging*methods,*on*the*other*hand,*are*unique*in*their*combination*of*good*

temporal*and*spatial*resolution.*This*allows*for*precise*localization*of*dynamic*changes*in*

brain*activity,*providing*unified*spatiotemporal*neurophysiological*data*that*could*prove*

critical*in*differentiating*one*form*of*meditation*practice*from*another.*

Taken*together,*our*central*aims*were*to:*(i)*comprehensively*review*and*meta_

analyze*the*existing*functional*neuroimaging*studies*of*meditation*(using*the*meta_analytic*

method*known*as*activation*likelihood*estimation,*or*ALE),*and*compare*consistencies*in*

brain*activation*and*deactivation*both*within*and*across*psychologically*distinct*

meditation*techniques;*(ii)*examine*the*magnitude*of*the*effects*that*characterize*these*

activation*patterns,*and*address*whether*they*suggest*any*practical*significance;*and*(iii)*

articulate*the*various*methodological*challenges*facing*the*emerging*field*of*contemplative*

neuroscience*(Caspi*and*Burleson,*2005,*Thompson,*2009,*Davidson,*2010,*Davidson*and*



Kaszniak,*2015),*particularly*with*respect*to*functional*neuroimaging*studies*of*

meditation.*

*

Figure!1.!!!The!rapid*increase*in*functional*(fMRI*and*PET)*and*morphometric*

neuroimaging*of*meditation*and*related*secular*contemplative*practices.+

*Functional*neuroimaging*(fMRI*and*PET)*study*counts*based*on*the*results*of*the*present*review;*morphometric*study*counts*based*on*our*previous*meta_analysis*of*this*literature*(Fox*et*al.,*2014).+!

!

1.1!Functional!neuroimaging!of!meditation:!The!need!for!quantitative!meta8analysis+

There*are*now*close*to*a*hundred*functional*neuroimaging*studies*of*meditation*

(Fig.*1)*–*but*can*any*conclusions*be*drawn*from*this*large*and*fast*growing*literature?*

Determining*reliable*neural*correlates*of*any*mental*process*is*a*difficult*task*under*the*

best*of*conditions.*This*is*all*the*more*true*when*the*mental*processes*in*question*are*



subtle*and*largely*subjective,*and*when*the*participants*employed*are*highly*experienced*

practitioners*often*operating*within*spiritual_religious*frameworks.*Despite*the*

voluminous*functional*neuroimaging*literature*on*meditation,*we*suspect*that*most*

researchers*would*be*hard_pressed*to*provide*a*clear*answer*to*the*ostensibly*simple*

question:*What*brain*regions*are*reliably*recruited,*for*instance,*by*focused*attention*

meditation?*We*expect*that*similar*challenges*would*face*researchers*seeking*to*describe*

other*common*categories*of*meditation.*Part*of*the*problem*is*that*despite*the*rapid*

proliferation*of*neuroimaging*studies*of*meditation*in*the*past*few*years*(Fig.*1),*neither*

narrative*(Rubia,*2009,*Tang*et*al.,*2015),*nor*meta_analytic*(Sedlmeier*et*al.,*2012,*Fox*et*

al.,*2014),*nor*theoretical*(Holzel*et*al.,*2011,*Vago*and*Silbersweig,*2012)*synthesis*of*

these*results*has*been*able*to*keep*pace*with*the*emergence*of*new*and*complex*data.*

Given*the*numerous*and*often*contradictory*results*reported*to*date,*researchers*

interested*in*the*neural*correlates*of*meditation*may*find*it*difficult*to*decide*among*

different*findings.*As*experts*on*meta_analytic*methodology*recently*framed*the*general*

problem*of*integrating*findings:**

How*should*scientists*proceed*when*results*differ?*First,*it*is*clear*how*they*should*not!proceed:*they*

should*not*pretend* that* there* is*no*problem,*or*decide* that* just*one*study*(perhaps* the*most*recent*

one,*or*the*one*they*conducted,*or*a*study*chosen*via*some*other*equally*arbitrary*criterion)*produced*

the*correct*finding.*If*results*that*are*expected*to*be*very*similar*show*variability,*the*scientific*instinct*

should*be*to*account*for*the*variability*by*further*systematic*work.**(Cooper*and*Hedges,*2009);*p.*4)**

It*is*in*this*spirit*of*systematic,*quantitative*synthesis*that*the*present*meta_analysis*was*

conducted.*

Although*the*coordinate_based*meta_analysis*we*employed*here*(see*Methods)*is*

far*from*the*perfect*(or*only)*method*of*achieving*this*kind*of*synthesis*(Salimi_Khorshidi*



et*al.,*2009),*it*is*a*major*improvement*over*narrative*(and/or*selective)*surveys*of*the*

literature,*which*often*lead*to*erroneous*conclusions*(Schmidt,*1992).*We*therefore*echo*

other*neuroscientists*in*arguing*that*quantitative*meta_analysis*of*neuroimaging*data*is*a*

potent*(indeed*necessary)*tool*for*better*understanding*the*neural*basis*of*mental*

processes*(Wager*et*al.,*2007,*Salimi_Khorshidi*et*al.,*2009,*Wager*et*al.,*2009,*Kober*and*

Wager,*2010,*Yarkoni*et*al.,*2010,*Hupé,*2015).*More*specifically,*meta_analysis*can*

provide:*(i)*a*less_biased*overview*of*an*evidence*base*than*a*simple*narrative*review*or*

qualitative*survey*of*prior*work*(Schmidt,*1992);*(ii)*specific*peaks*of*meta_analytic*

activation,*rather*than*just*broad*regional*results;*(iii)*statistically*significant*activation*

overlaps*across*studies,*instead*of*merely*indicating*broad*‘replications’;*and*(iv)*a*way*to*

mitigate*the*lack*of*statistical*power*caused*by*small*samples*found*in*many*neuroimaging*

studies*–*a*problem*especially*prevalent*in*the*study*of*meditation*practitioners,*where*

experienced*individuals*are*difficult*to*recruit.*For*a*deeper*discussion*of*the*limitations*of*

these*meta_analytic*methods,*however,*see*Section*5.11.**

* Moreover,*persuasive*arguments*have*also*been*made*for*a*move*toward*a*more*

‘cumulative’*science*that*focuses*on*broad*conclusions*drawn*from*dozens*or*hundreds*of*

independent*investigations,*as*opposed*to*‘critical*experiments’*from*isolated*but*

influential*studies*(Schmidt,*1992,*Yarkoni*et*al.,*2010).*Some*statisticians*have*gone*as*far*

as*claiming*that*“any*individual*study*must*be*considered*only*a*single*data*point*to*be*

contributed*to*a*future*meta_analysis”*(Schmidt,*1992);*p.*1179).*Without*endorsing*such*

an*extreme*viewpoint,*we*agree*that*a*careful*sifting*and*quantitative*synthesis*of*the*

research*conducted*to*date*will*help*to*advance*the*state*of*the*field.*

!



1.2!Four!general!categories!of!meditation!

Before*conducting*a*synthesis*of*the*meditation*neuroimaging*literature,*one*must*

ask*a*central*question:*How*are*meditation*practices*to*be*categorized?*There*is*growing*

consensus*that*at*least*three*broad*categories*of*meditation*techniques*can*be*discerned:*

focused!attention,*open!monitoring,*and*compassion*or*loving8kindness*practices*(Cahn*and*

Polich,*2006,*Lutz*et*al.,*2008b,*Brewer*et*al.,*2011,*Vago*and*Silbersweig,*2012,*Lippelt*et*

al.,*2014).*Similar*classification*schemes*appear*to*reach*back*centuries*to*early*Eastern*

treatises*on*meditation*(Harvey,*1990,*Lodro,*1998,*Goenka,*2000,*Wangyal*and*Turner,*

2011).*Although*a*few*broad*categories*do*not*begin*to*exhaust*the*subtleties*of*all*

contemplative*practices*(Niranjananada,*1993,*Singh,*2002),*there*seems*to*be*fair*

justification*for*a*tentative*division*along*these*lines*(Lutz*et*al.,*2008b,*Vago*and*

Silbersweig,*2012).*The*main*aim*of*this*review*and*meta_analysis*was*to*investigate*

whether*some*isomorphism*(even*if*a*complex*one)*can*be*discovered*between*

psychological*practices*and*brain*recruitment*(Cacioppo*and*Tassinary,*1990):*that*is,*are*

these*various*categories*of*meditation,*which*differ*markedly*at*the*psychological*level*

(Ψ),*in*fact*characterized*by*distinctive*patterns*of*brain*activation*and*deactivation*(Φ)?*

1.2.1+Focused+attention+meditation.!Focused!attention*meditation*involves*

directing*attention*to*one*specific*object*(e.g.,*the*breath*or*a*mantra)*while*monitoring*

and*disengaging*from*extraneous*thoughts*or*stimuli*(Harvey,*1990,*Hanh,*1991,*Kabat_

Zinn,*2005,*Lutz*et*al.,*2008b,*Wangyal*and*Turner,*2011).*Attention*is*directed*to*a*

particular*object*(most*commonly*the*sensations*associated*with*respiration),*and*

whenever*the*mind*wanders,*attention*is*redirected*to*this*target.*With*regular*training,*

the*ability*to*voluntarily*control*attention*without*being*distracted*appears*to*become*



progressively*enhanced*(e.g.,*(MacLean*et*al.,*2010)*and*less*effortful*(Wallace,*1999,*2006,*

Brefczynski_Lewis*et*al.,*2007).*In*particular,*focused*attention*meditation*may*lead*to*

three*types*of*improvements:*monitoring*the*locus*of*attention,*disengaging*from*

distraction,*and*shifting*attention*back*to*its*intended*target*(Lutz*et*al.,*2008b).*

* 1.2.2+Mantra+recitation+meditation.*Focused*attention*meditation*itself*may*be*

subdivided*into*distinct*practices,*or*distinguished*from*practices*that*appear*similar*at*

first*glance:*in*particular,*mantra!recitation!meditation*involves*unique*components*

(Travis,*2014).*Mantra*meditation*–*probably*best*known*in*the*form*of*the*widespread*

‘Transcendental*Meditation’*–*involves*the*repetition*of*a*sound,*word,*or*sentence*(spoken*

aloud*or*silently*in*one's*head)*with*the*goals*of*calming*the*mind,*maintaining*focus,*and*

avoiding*mind_wandering.*While*mantra*meditation*therefore*clearly*overlaps*with*other*

forms*of*focused*attention*in*regard*to*its*aims,*it*differs*in*that*the*object*of*focus*is*a*

voluntary*verbal_motor*production,*rather*than*naturally*arising*body*sensations*(like*the*

breath)*or*external*physical*objects*(such*as*a*point*in*space*upon*which*the*gaze*is*

focused).*Further,*mantra*meditation*appears*to*be*associated*with*neural*correlates*

separate*from*other*related*forms*of*focused*attention*practice*(e.g.,*(Lazar*et*al.,*2000,*

Shimomura*et*al.,*2008,*Davanger*et*al.,*2010,*Tomasino*et*al.,*2013)*–*although,*in*the*

absence*of*a*meta_analysis,*these*differences*remain*only*suggestive.*Although*mantra*

meditation*could*reasonably*be*placed*within*the*general*‘focused*attention’*category*of*

practices,*because*of*its*unique*elements*(most*notably*its*linguistic,*verbal_motor*

component)*we*examined*it*separately*here.*

1.2.3+Open+monitoring+meditation.+Open!monitoring!practice*typically*begins*with*

bringing*attention*to*the*present*moment*and*impartially*observing*all*mental*contents*



(thoughts,*emotions,*sensations,*etc.)*as*they*naturally*arise*and*subside.*A*key*element*of*

this*practice*is*possessing*an*open,*accepting*attitude*toward,*and*learning*to*‘let*go’*of,*

mental*content*–*neither*resisting*nor*elaborating*upon*anything*that*surfaces*in*

awareness*(Harvey,*1990,*Walker,*1995,*Suzuki,*2003,*Kabat_Zinn,*2005,*Wangyal*and*

Turner,*2011).*In*contrast*to*focused*attention,*then,*in*open*monitoring*meditation*mental*

content*is*neither*evaluated*for*relevance*to*a*particular*goal,*nor*is*any*content*

suppressed.*This*‘non_elaborative’*mental*stance*cultivates*a*more*present_centered*

awareness*in*tune*with*the*moment_to_moment*experience*of*the*mind*and*body*(Anālayo,*

2003,*Farb*et*al.,*2007).*Somatic*and*visceral*body*sensations*are*often*a*prominent*feature*

of*this*present*moment*experience,*and*hence*interoceptive*and*exteroceptive*inputs*

generally*receive*greater*processing*in*open*monitoring*than*in*focused*attention*practices*

(e.g.,*(Fox*et*al.,*2012,*Kerr*et*al.,*2013).*Open*monitoring*meditation*can*also*sometimes*

serve*as*a*platform*from*which*practitioners*can*go*on*to*enter*subtler*states*of*non_dual*

awareness*(see*section*1.3,*below).*

1.2.4+Loving?kindness+and+compassion+meditations.+Loving8kindness*meditation*

(closely*related*to,*but*not*identical*with,*compassion*meditation)*aims*to*deepen*feelings*

of*sympathetic*joy*for*all*living*beings,*as*well*as*promote*altruistic*behaviors*(Harvey,*

1990,*Gyatso*and*Jinpa,*1995,*Kabat_Zinn,*2005,*Lutz*et*al.,*2008a).*Typically,*practitioners*

begin*by*generating*feelings*of*kindness,*love,*and*joy*toward*themselves,*then*

progressively*extend*these*feelings*to*imagined*loved*ones,*acquaintances,*strangers,*

enemies,*and*eventually*all*living*beings*(Harvey,*1990,*Kabat_Zinn,*2005,*Lutz*et*al.,*

2008a).*Compassion*meditation*generally*takes*this*practice*a*step*further:*practitioners*

imagine*the*physical*and/or*psychological*suffering*of*others*(ranging*from*loved*ones*to*



all*humanity)*and*cultivate*compassionate*attitudes*and*responses*to*this*suffering.*Both*

practices*share*the*long_term*goals*of*enhancing*sympathetic*joy*and*empathy*for*pain,*

which*are*viewed*as*trainable*skills*that*increase*altruistic*behavior*(Gyatso*and*Jinpa,*

1995,*Lutz*et*al.,*2008a).*Although*there*are*potentially*important*psychological*

differences*between*these*practices,*of*the*neuroimaging*studies*to*date,*the*instructions*

have*been*comparable:*participants*have*been*asked*to*generate*positive*emotions*(such*

as*loving_kindness,*well_wishing,*or*compassion)*directed*toward*others*and/or*generated*

in*a*non_referential*way*(see*the*supplementary*material*for*the*exact*instructions*in*each*

study).*We*therefore*grouped*the*available*studies*together,*reasoning*that*they*were*

more*similar*than*different:*despite*some*difference*in*instructions*and*implementation*of*

the*practices,*all*studies*involved*a*strong*focus*on*cultivating*positive*affect*directed*

outward.*We*acknowledge,*however,*that*differences*in*the*various*stages*of*these*

practices*(e.g.,*compassion*for*self,*vs.*a*loved*one,*vs.*a*stranger,*vs.*non_referential*

compassion)*might*very*well*be*resolved*at*the*neural*level*by*future*research**Note,*too,*

that*the*instructions*involved*in*the*studies*investigated*here*do*not*exhaust*the*possibility*

of*this*type*of*practice,*which*can*also*involve*complex*visualizations*and*a*focus*on*

spiritual*‘benefactors’*(Makransky*et*al.,*2012).*Further*research*is*clearly*warranted*to*

more*thoroughly*examine*the*many*variants*of*loving_kindness*and*compassion*

meditation.*

In*one*sense,*loving_kindness*and*compassion*meditations*could*also*be*considered*

a*form*of*focused!attention*in*that*they*often*focus*intensively*on*a*single*object*(the*person*

who*is*the*target*of*the*loving_kindness)*and*cultivate*a*consistent*emotional*tone*(to*the*

exclusion*of*other*kinds*of*affect).*Alternatively,*when*conducted*in*a*non_referential,*all_



embracing*way*(extending*one’s*compassion*and*joyful*feelings*to*any*being*or*object*that*

arises*in*consciousness*indiscriminately,*or*even*cultivating*such*feelings*without*any*

object*whatsoever),*these*practices*could*conceivably*be*considered*a*form*of*open!

monitoring.*Nonetheless,*given*the*strong*emphasis*on*deliberate*cultivation*of*joyful,*

altruistic,*and*empathetic*emotions*that*is*fairly*unique*to*these*practices,*there*seems*

sufficient*justification*for*considering*them*as*a*separate*class,*worthy*of*investigation*in*

its*own*right.*

*

1.3!Other!forms!of!meditation!

It*is*important*to*note*that*these*four*putative*categories*of*meditation*are*intended*

not*as*a*final*classification*scheme,*but*merely*as*a*first*step*toward*delineating*

quantitative*neurophysiological*(Φ)*correlates*associated*with*relatively*distinctive*

psychological*(Ψ)*practices*(Cacioppo*and*Tassinary,*1990).*There*are*several*other*major*

categories*of*meditation*that*have*been*investigated*in*some*preliminary*work,*but*that*

could*not*be*examined*meta_analytically*due*to*a*paucity*of*data.*We*nonetheless*sought*to*

examine*and*compare*our*meta_analytic*results*with*these*data*by*conducting*a*qualitative*

review*of*the*results*reported*to*date.**

Visualization*meditation,*for*instance,*involves*creating*and*sustaining*complex*

mental*imagery*for*extended*periods*of*time.*These*visualizations*typically*involve*

mandalas*or*yantras*(geometric*designs)*or*deities*or*patron_teachers*(Gyatso,*1981),*and*

experts*in*these*techniques*have*been*shown*to*have*enhanced*visuospatial*processing*

(Kozhevnikov*et*al.,*2009).*Nonetheless,*only*a*single*study*of*which*we*are*aware*has*

investigated*the*neural*correlates*of*any*form*of*visualization*meditation*(Lou*et*al.,*1999),*



although*loving_kindness*and*compassion*practices*can*also*sometimes*involve*important*

visualization*components*(Weng*et*al.,*2013).*

Another*almost*uninvestigated*set*of*practices*based*in*yogic*traditions*involve*the*

withdrawal*of!the!senses!(pratyahara*in*Sanskrit;*(Iyengar,*2005).*These*practices*involve*

the*deliberate*detachment*from*or*blocking*of*sensory*inputs,*including*pain,*with*the*

eventual*goal*of*transcending*any*narrow*sense*of*self*or*personal*identity.*Although*this*

type*of*practice*shares*many*features*of*focused*attention*techniques*(e.g.,*a*highly*

selective*attentional*focus),*and*would*traditionally*be*practiced*alongside*them*(Iyengar,*

2005),*it*could*also*be*considered*a*practice*in*its*own*right.*However,*so*far*only*one*

study*has*investigated*neural*correlates*of*this*kind*of*technique*(Kakigi*et*al.,*2005).*

Non8dual!awareness!practices*are*another*example.*In*general,*the*aim*of*these*

practices*is*to*dissolve*or*attenuate*the*boundary*between*subject*and*object*(Josipovic,*

2010,*Travis*and*Shear,*2010b,*Dunne,*2011).*Although*this*kind*of*practice*bears*some*

resemblance*to*open*monitoring*meditation,*it*could*be*considered*a*distinct*practice,*and*

further*investigation*into*its*neural*correlates*would*be*a*welcome*follow_up*to*a*recent,*

seminal*study*(Josipovic*et*al.,*2011,*Josipovic,*2014).*

Finally,*another*suite*of*practices*aims*at*manipulating*or*enhancing*meta_

awareness*during*various*stages*of*sleep*and*dreaming.*Yoga!nidra*(literally*‘sleep*yoga’),*

for*instance,*involves*the*deliberate*dampening*of*sensory*inputs*to*induce*a*‘hypnagogic’*

state*(Mavromatis,*1987,*Hori*et*al.,*1994,*Hayashi*et*al.,*1999,*Stenstrom*et*al.,*2012),*so*as*

to*enhance*one’s*capacity*to*carry*out*visualization*and*relaxation*practices*(Saraswati,*

1984).*Dream!yoga*(rmi8lam*in*Tibetan;*svapnadarsana*in*Sanskrit)*practices*aim*at*

enhancing*meta_awareness*during*dreaming*(i.e.,*enhancing*so_called*‘lucid’*dreaming;*



(Gackenbach*and*LaBerge,*1988),*and*are*particularly*prevalent*in*the*Tibetan*Buddhist*

tradition*(Norbu*and*Katz,*1992,*Mullin,*1996,*Rinpoche,*2004).*Other*techniques*even*aim*

at*maintaining*awareness*during*states*of*deep,*dreamless*sleep*(Aurobindo,*2004,*

Sharma,*2012).*We*are*aware*of*only*a*single*study*of*these*practices,*however*(Kjaer*et*al.,*

2002).*

+

1.4!Delineating!reliable!neural!correlates!of!different!meditation!practices!

Only*in*about*the*past*year*have*a*sufficient*number*of*studies*been*cumulatively*

reported*to*allow*for*a*reliable*meta_analysis*of*each*major*meditation*type*(including*

open*monitoring*and*loving_kindness/compassion*meditations).*Even*very*recent*meta_

analyses*have*been*forced*by*a*paucity*of*empirical*data*to*examine*only*focused*attention*

and*mantra*recitation*meditation*(Tomasino*et*al.,*2013),*or*to*group*all*practice*types*

together*(Sperduti*et*al.,*2012).*Other*meta_analyses*have*employed*less*theoretically*or*

empirically*grounded*categorizations,*such*as*basing*meta_analytic*contrasts*on*the*

religion*of*origin*for*a*practice*(Buddhism*vs.*Hinduism)*as*opposed*to*the*

phenomenological*content,*intended*goals,*and*behavioral*characteristics*of*the*practice*

itself*(Tomasino*et*al.,*2014).*

Here*we*present*the*first*meta_analysis*inclusive*of*four*major*categories*of*

meditation,*with*a*focus*on*elucidating*whether*ostensibly*distinct*forms*of*mental*

practice*activate*a*common*neural*substrate*(Sperduti*et*al.,*2012)*or*instead*show*

dissociable*patterns*of*underlying*neural*activation*and*deactivation.*Accordingly,*we*

conducted*four*separate*activation*likelihood*estimation*(ALE)*meta_analyses*using*263*

foci*of*peak*activation*from*26*independent*PET*and*fMRI*studies*involving*32*unique*



experiments*(Tables*1*and*2)*to*examine*the*patterns*of*brain*activation*associated*with*

focused*attention,*mantra*recitation,*open*monitoring,*and*loving_kindness/compassion*

meditation.*Additionally,*we*examined*the*results*for*three*categories*of*meditation*that*

have*only*been*investigated*thus*far*in*a*single*study*each*(Table*1).*Because*this*paucity*

of*data*precluded*a*formal,*quantitative*meta_analysis,*we*qualitatively*reviewed*the*

results*for*each*practice*type*and*compared*it*to*our*other*meta_analytic*results*(Table*1).*

*

!Table!1.***Seven*meditation*categories*investigated*via*quantitative*meta_analysis*and*

qualitative*review.!

Meditation+Type+ Contributing+Experiments+(N)+

Contributing+Foci++A/D+(Total)+

Quantitative*meta_analysis*

Focused*attention* 7* 48/13*(61)*

Mantra*recitation* 8* 63/19*(82)*

Open*monitoring* 10* 45/29*(74)*

Compassion/Loving_kindness** 6* 36/4*(40)*

+++Totals* 31* 192/65*(257)*

Qualitative*review*

Visualization* 1* –*

Sense_withdrawal* 1* –*

Non_dual*awareness* 1* –*Note.*Some*studies*examined*multiple*meditation*types*and*therefore*contributed*to*multiple*analyses.*This*resulted*in*a*total*of*31*experiments*(contrasts)*from*the*25*independent*studies*included*in*the*quantitative*meta_analyses*for*the*first*four*categories*(see*Table*2*for*details*of*included*studies).*Further,*three*other*categories*of*meditation*were*also*examined*where*results*have*been*reported*from*only*a*single*study*to*date.*These*investigations*were*not*included*in*any*formal,*quantitative*meta_analyses,*but*the*results*were*nonetheless*examined*and*compared*with*our*meta_analytic*findings*in*a*qualitative*fashion.*A*=*activations;*D*=*deactivations.*+

+

!

!



1.5!Are!the!effects!of!meditation!practices!on!brain!function!of!any!practical!significance?!

Determining*whether*there*are*any*consistencies*in*brain*activation*for*various*

styles*of*meditation*is*only*the*first*step.*A*logical*next*question*is*whether*activations*and*

deactivations*associated*with*a*given*meditation*technique*have*any*practical*significance.*

That*is,*what*effect*sizes*characterize*these*differences,*and*do*effect*sizes*vary*across*

particular*forms*of*meditation?*Note,*however,*that*practical*significance*is*not*a*fully*

objective*measure*–*typically*a*half_standard*deviation*difference*is*considered*a*notable*

effect,*but*this*boundary*is*essentially*arbitrary,*and*‘practical’*significance*does*not*

necessarily*translate*to*clinical*significance*or*relevance*(Rosnow*and*Rosenthal,*1989).*

An*additional*benefit*of*calculating*effect*sizes*is*that*they*can*be*used*to*estimate*

the*extent*of*publication*bias*in*a*field*(Egger*et*al.,*1997),*a*major*and*outstanding*issue*

across*the*social*and*neurobiological*sciences,*including*contemplative*neuroscience.*

Because*we*found*strong*evidence*for*publication*bias*in*morphometric*(anatomical)*

neuroimaging*studies*of*meditation*in*a*recent*review*(Fox*et*al.,*2014),*we*sought*to*

address*whether*or*not*such*a*bias*might*be*affecting*functional*neuroimaging*studies*of*

meditation*as*well.*The*second*central*aim*of*this*meta_analytic*synthesis*was*therefore*to*

provide*preliminary*estimates*of*effect*sizes*in*the*functional*neuroimaging*of*meditation*

in*order*to*assess*practical*significance*and*the*possibility*of*publication*bias.



2.+Meta?analytic+methods*

!

2.1!Literature!review!

2.1.1+Search+strategy.+Three*authors*(KCRF,*SN,*and*MG)*searched*MEDLINE*

(http://www.ncbi.nlm.nih.gov/pubmed/),*Google*Scholar*(http://scholar.google.com),*and*

PsycINFO*(http://www.apa.org/pub/databases/psycinfo/index.aspx)*for*all*papers*

containing*the*word*‘meditation’*since*the*first*functional*neuroimaging*study*of*

contemplative*practices*was*published*(Lou*et*al.,*1999).*These*extensive*lists*of*articles*

were*then*refined*by*searching*within*results*for*studies*that*contained*any*of*the*words*

or*phrases*‘magnetic*resonance*imaging’,*‘MRI,’*‘neuroimaging,’*or*‘brain’*within*the*title*or*

abstract.*Of*the*remaining*results,*every*abstract*was*consulted*to*see*whether*the*study*

actually*employed*functional*neuroimaging*methods*to*study*meditation.*The*reference*

lists*of*each*study*found,*as*well*as*those*of*several*major*reviews*(e.g.,*(Holzel*et*al.,*2011,*

Vago*and*Silbersweig,*2012)),*were*also*consulted*to*ensure*that*no*studies*were*missed.*

2.1.2+Study+inclusion+and+exclusion+criteria.+All*studies*using*functional*

neuroimaging*to*investigate*some*form*of*meditation*were*considered.*By*‘functional*

neuroimaging’*we*mean*functional*magnetic*resonance*imaging*(fMRI)*or*positron*

emission*tomography*(PET)*studies*that*can*provide*details*about*the*specific*location*of*

brain*activations*and*deactivations.*Using*the*search*strategy*detailed*above,*a*total*of*78*

studies*served*as*the*initial*pool*of*data*to*be*reviewed*(see*Table*2*for*included*studies,*

and*Table*S1*for*excluded*studies).+

* In*order*to*ensure*the*most*rigorous*results*possible,*stringent*inclusion*criteria*

were*applied.*Studies*were*required*to:*(i)*report*specific*peak*foci*of*activation*in*either*



Talairach*or*Montreal*Neurological*Institute*(MNI)*space;*(ii)*include*a*reasonable*sample*

size*(i.e.,*case*studies*of*single*subjects*were*excluded);*(iii)*involve*participants*who*

actually*practiced*meditation,*be*they*novices*or*long_term*practitioners*(as*opposed*to,*

for*example,*studies*involving*only*self_report*scales*of*‘dispositional’*mindfulness);*(iv)*

involve*actual*meditation*during!the!scanning!session*(as*opposed*to*having*meditation*

practitioners*engage*in*other*tasks*without*some*explicit*contemplative*element);*and*(v)*

involve*healthy,*non_clinical*populations.*Finally,*(vi)*only*reports*published*in*peer_

reviewed*scientific*journals*were*included*(results*from*conference*abstracts,*presented*

talks,*dissertations,*etc.,*were*excluded).*For*further*details*on*excluded*studies,*see*the*

Supplementary*Material*Methods.*

Ultimately,*about*one*third*(25*of*78)*of*the*examined*studies*were*included*in*our*

meta_analyses*(Table*2).*Given*that*some*of*these*studies*examined*multiple*categories*of*

meditation,*we*investigated*a*total*of*31*separate*‘experiments’*or*contrasts*of*interest*

spread*across*the*four*major*meditation*categories.*

2.1.3+Study+classification.+Two*coders*with*longtime*personal*meditation*

experience*(authors*KCRF*and*MLD)*independently*classified*all*included*results*as*

involving*focused!attention,*open!monitoring,*compassion*or*loving8kindness,*or*mantra!

recitation*meditation.*Concordance*was*nearly*perfect:*a*single*disparity*was*resolved*after*

further*discussion.*Several*studies*employed*multiple*practice*types*across*different*

sessions;*in*these*cases,*results*from*each*session*were*coded*separately*and*considered*

individual*‘experiments.’*Therefore,*the*number*of*‘experiments’*exceeded*the*number*of*

independent*studies*actually*included*in*the*meta_analysis*(see*Tables*1*and*2).*All*

classifications*for*included*studies*are*summarized*in*Table*2.**



Further,*one*study*each*was*found*that*examined*visualization*(Lou*et*al.,*1999),*

sense8withdrawal*(Kakigi*et*al.,*2005),*and*non8dual!awareness*(Josipovic*et*al.,*2011)*forms*

of*meditation.*Again,*both*coders*(KCRF*and*MLD)*independently*classified*and*agreed*on*

these*categorizations.*Due*to*there*being*only*a*single*study*for*each*category,*these*

reports*were*not*included*in*any*formal*meta_analyses.*Nevertheless,*their*results*were*

qualitatively*reviewed*and*considered*in*comparison*to*our*meta_analytic*results*for*the*

other*four*general*meditation*styles*(see*Table*1).*

In*virtually*all*cases,*classification*was*straightforward*and*mirrored*the*

classifications*described*by*the*authors*of*the*studies*in*their*methods.*For*instance,*

phrases*such*as*‘concentration*meditation’*were*categorized*under*the*focused*attention*

category;*mantra*meditation*studies*were*easily*categorized*based*on*descriptions*of*

mantra*recitation*in*the*methods;*and*so*on.*Because*of*the*prevalence*of*classification*

schemes*involving*the*four*categories*described*above*(e.g.,*(Cahn*and*Polich,*2006,*Lutz*et*

al.,*2008b,*Travis*and*Shear,*2010a,*Vago*and*Silbersweig,*2012),*many*studies*in*fact*

explicitly*described*their*methods*using*these*same*(or*highly*similar)*terms.*

*

! !



Table!2.***Studies*included*in*the*meta_analyses*(n!=*25).**

Study+ Practice++ N+(M/C)+ Tradition+ Expertise+ Average+Experience+Lou*et*al.*(1999)* OM*+*LK** 9/–* Yoga*Nidra* LTP* >5*yrs*Lazar*et*al.*(2000)* MR* 5/–* Kundalini* LTP* 4*yrs*Brefczynski_Lewis*et*al.*(2007)* FA* 14/16* Tibetan*Buddhist* LTP* 19000*hrs*&*44000*hrs*

Farb*et*al.*(2007)* OM* 20/–* MBSR* STT* ~42*hours*Lutz*et*al.*(2008)* LK* 16/16* Tibetan*Buddhist* LTP* 45*±*12.7*yrs*Shimomura*et*al.*(2008)* MR* 8/–* Pure*Land*Buddhism** LTP* >10*years*

Lutz*et*al.*(2009)* LK* 10/12* Tibetan*Buddhist* LTP* 40*±*9.6*yrs*Davanger*et*al.*(2010)* MR* 4/–* Acem*Meditation* LTP* >23*yrs*

Engström*et*al.*(2010)* MR* 8/–* Acem*Meditation*

and*Kundalini*Yoga* LTP* 1.17*yrs*

Manna*et*al.*(2010)* FA*+*OM* 8/–*Vipassana*

(Theravada*_*Thai*Forest*Tradition)*

LTP* 15750*hrs*

Brewer*et*al.**(2011)* FA*+*OM*+*LK* 12/13* Vipassana*

(Mindfulness)* LTP* 10565*±*5148*hrs*Gard*et*al.*(2011)* OM* 17/17* Vipassana* LTP* 5979*±*5114*Ives_Deliperi*et*al.*(2011)* OM* 10/–* MBSR* LTP* >4*yrs*

Kalyani*et*al.*(2011)* MR* 12/–* Om*mantra*recitation* LTP*+*STT* Not*reported*

Taylor*et*al.*(2011)* OM* 12/10* Zen* LTP*+*STT* LTP:*>1,000*hrs*STT:*1*wk*

Wang*et*al.*(2011)* MR* 10/–* Kundalini*yoga* LTP* ~20,000*hrs*Dickenson*et*al.**(2012)* FA* 31/–* Mindfulness/MBSR* STT* No*previous*experience;*brief*

meditation*induction*only**Hasenkamp*et*al.*(2012)* FA* 14/–* Various* LTP* 1386*±*1368*hrs*

Lee*et*al.*(2012)* FA*+*LK* 22/22* Theravada* LTP* FA:*5249*±*6192*hrs**LK:*7492*±*6681*hrs*

Farb*et*al.*(2013)* OM* 20/16* MBSR* STT* 49.2*±*4.3*hrs*Guleria*et*al.*(2013)* MR* 14/–* Soham*Meditation* LTP* 2088*±*320*hrs*Lutz*et*al.*(2013)* OM* 14/14* Tibetan*Buddhist* LTP* 27000*±*12500*hrs*Weng*et*al.*(2013)* LK* 20/21* Tibetan*Buddhist* STT* 5.9*±*0.5*hrs*Lutz*et*al.*(2014)* OM* 24/22* Mindfulness/MBSR* STT* Variable*Xu*et*al.*(2014)* FA*+*MR* 14/–* Acem*Meditation* LTP* 27*±*9*yrs*All*studies*employed*fMRI*except*for*Lou*et*al.*(1999),*which*employed*PET.*C:*controls;*FA:*focused*attention;*LK:*loving_kindness*or*compassion*meditation;*LTP:*long_term*practitioners;*M:*meditators;*MBSR:*mindfulness_based*stress*reduction;*MR:*mantra*recitation;*N:*sample*size;*OM:*open*monitoring;*STT:*short_term*training.*!!!! !



2.2!The!question!of!baselines,!control!conditions,!and!tasks!engaged!in!during!meditation!

* One*potential*problem*is*that*even*studies*examining*a*similar*form*of*meditation*

might*compare*a*meditation*practice*to*very*different*baseline*or*comparison*tasks*and*

conditions.*However,*collapsing*across*numerous*different*baselines*or*control*conditions*

is*a*common*(in*fact,*usually*inevitable)*practice*in*meta_analyses*of*functional*

neuroimaging*studies*(Turkeltaub*et*al.,*2002,*Wager*et*al.,*2003,*Wager*et*al.,*2007,*Wager*

et*al.,*2009,*Caspers*et*al.,*2010,*Yarkoni*et*al.,*2010,*Tomasino*et*al.,*2013).+It*is*by*no*

means*a*problem*limited*to*the*meditation*literature.*Aside*from*the*heterogeneity*of*

conditions*across*studies,*meditation*is*also*often*investigated*during*a*given*task*or*form*

of*stimulus*presentation.*Although*typically*these*tasks*or*stimuli*are*equally*present*in*

the*baseline*or*control*condition*(and*therefore,*in*principle,*should*not*unduly*influence*

the*meditation*state*results),*the*potential*for*our*results*representing*interactions*

between*meditation*and*the*given*task*employed*should*be*kept*in*mind.*These*issues*are*

examined*further*in*the*Discussion.*

The*goal*of*the*present*synthesis*was*to*determine,*irrespective*of*any*incidental*

differences*in*comparison*or*baseline*conditions*and*tasks:*(i)*whether*differing*

meditation*practices*tend*to*reliably*recruit*differentiable*neural*networks;*(ii)*if*the*

differences*in*brain*activation*show*practically*significant*effect*sizes;*and*lastly,*(iii)*

whether*distinct*practices*exhibit*differing*mean*effect*sizes*(i.e.,*is*a*given*style*of*

meditation*associated*with*greater*differences*in*brain*activity*than*others?).*

!

!

!



2.3!Reporting!and!classification!of!results!!

* All*peak*voxel*coordinates*are*reported*in*Montreal*Neurological*Institute*(MNI)*

space.*For*consistency,*for*all*studies*where*peak*voxels*were*originally*reported*in*

Talairach*coordinates,*we*used*the*WFU*Pickatlas*software*package*(Maldjian*et*al.,*2003)+

to*perform*a*nonlinear*transformation*of*Talairach*coordinates*to*MNI*space.*For*meta_

analytic*ALE*results,*region*classifications*follow*those*indicated*in*the*Multi_Image*

Analysis*GUI*(‘Mango’)*image_viewing*software*(UT*Health*Science*Center*Research*

Imaging*Institute)*used*to*display*our*findings*(see*Results*below).*For*additional*

precision,*the*Duvernoy*neuroanatomical*atlas*was*also*consulted*(Duvernoy*et*al.,*1991).*

!

2.4!Activation!likelihood!estimation!(ALE)!meta8analysis!

* 2.4.1+General+methods.+We*used*a*quantitative,*random_effects*meta_analytic*

method*known*as*activation*likelihood*estimation*(ALE;*(Turkeltaub*et*al.,*2002,*Laird*et*

al.,*2005,*Eickhoff*et*al.,*2009,*Eickhoff*et*al.,*2012,*Turkeltaub*et*al.,*2012)*implemented*in*

the*software*program*GingerALE*2.1.1*(San*Antonio,*TX:*UT*Health*Science*Center*

Research*Imaging*Institute).+The*most*recent*ALE*algorithm*tests*for*above_chance*

clustering*of*peak*foci*from*different*experiments*included*in*the*meta_analysis*(Eickhoff*

et*al.,*2009,*Eickhoff*et*al.,*2012)*by*comparing*actual*activation*foci*locations/clustering*

with*a*null*distribution*that*includes*the*same*number*of*peak*foci*distributed*randomly*

throughout*the*brain.*Included*activation*foci*were*smoothed*using*a*full_width*half*

maximum*(FWHM)*Gaussian*kernel*dependent*on*the*total*sample*size*of*the*experiment*

from*which*foci*were*drawn*(larger*sample*_>*smaller*smoothing*kernel*–*empirically*

determined*by*(Eickhoff*et*al.,*2009,*Eickhoff*et*al.,*2012).*Resulting*statistical*maps*show*



clusters*where*convergence*between*foci*of*activation*or*deactivation*is*greater*than*

would*be*expected*by*chance*(i.e.,*if*foci*from*each*experiment*were*distributed*

independently).+

2.4.2+Primary+neuroimaging+meta?analyses.+We*meta_analyzed*a*total*of*257*

peak*foci*of*activation*or*deactivation*drawn*from*25*studies*(Table*2),*involving*

31separate*‘experiments’*or*contrasts*(summarized*in*Table*1).*In*order*to*retain*a*

maximal*amount*of*information,*this*primary*meta_analysis*collapsed*data*from*between_

group*(long_term*practitioners*vs.*novices*or*controls)*and*repeated_measures*(the*same*

practitioners*pre_*and*post_meditation*training)*designs.*Although*only*a*small*amount*of*

data*came*from*short_term*training*(STT)*investigations*(6*of*25*studies*included*in*the*

meta_analysis),*nonetheless*this*difference*presents*a*potentially*confounding*factor.*We*

therefore*addressed*this*issue*by*performing*supplemental*meta_analyses*that*included*

only*investigations*of*long_term*practitioners*(see*Supplementary*Materials).**

Several*coordinate*foci*(n!=*7)*from*the*included*studies*fell*outside*of*the*brain*

mask*templates*used*with*the*GingerALE*meta_analysis*software*(1*focus*for*focused*

attention*activations;*4*foci*for*open*monitoring*activations;*and*2*foci*for*loving_kindness*

activations).*This*is*a*normal*occurrence*when*using*exclusive*meta_analytic*template*

masks.*The*total*number*of*foci*included*in*the*final*meta_analyses*was*therefore*250.*

Statistical*maps*were*thresholded*using*a*false*discovery*rate*(FDR;*(Genovese*et*

al.,*2002)*of*q*=*.05*and*a*cluster*threshold*of*k*=*100*mm3.*The*meta_analytic*software*

offers*suggested*minimum*cluster*thresholds*depending*on*the*number*of*studies*and*foci*

entered.*These*recommendations*centered*around*100*(generally,*between*88*and*132*

mm3),*but*differed*slightly*in*each*of*our*eight*meta_analyses*(activations*and*



deactivations*for*each*of*four*meditation*categories).*For*consistency,*we*therefore*set*a*

standard*value*of*100*mm3*for*all*analyses.*Note*that*the*cluster*threshold*is*essentially*

arbitrary*and*does*not*affect*the*underlying*meta_analytic*analyses*or*results;*it*merely*

determines*which*meta_analytic*clusters*are*deemed*‘significant’*and*therefore*to*be*

reported*in*tables*of*results.*It*does*not*affect*the*underlying*meta_analytic*results,*which*

display*all*meta_analytic*activations*and*deactivations*regardless*of*cluster*threshold.*The*

full*meta_analytic*data*are*visible*in*our*supplementary*results*figures.*

To*display*our*results,*we*used*the*‘Colin’*template*brain*images*suggested*for*use*

with*GingerALE*2.1.1,*displayed*in*the*‘Mango’*software*package*(San*Antonio,*TX:*UT*

Health*Science*Center*Research*Imaging*Institute).*Maps*were*computed*separately*for*

activations*and*deactivations*for*each*meditation*category.*Activation*and*deactivation*

maps*were*then*concatenated*onto*a*single*template*brain*image*for*visualization*

purposes.*The*creation*of*the*final*figures*for*presentation*here*was*performed*in*the*

MRIcron*software*package*

(http://www.mccauslandcenter.sc.edu/mricro/mricron/index.html)*(Rorden*et*al.,*2007).*

!

2.5!Effect!size!meta8analysis!

In*addition*to*determining*which*brain*regions*were*consistently*activated*by*

various*meditation*practices,*we*sought*to*evaluate*the*magnitude*of*these*differences*(i.e.,*

their*effect*sizes;*(Cohen,*1992,*Lipsey*and*Wilson,*2001,*Sedlmeier*et*al.,*2012).*In*all,*17*

of*the*25*studies*that*met*our*inclusion*criteria*also*provided*necessary*and*sufficient*data*

to*allow*reliable*calculation*of*effect*sizes.**



Although*the*calculation*and*comparison*of*effect*sizes*in*neuroimaging*studies*

faces*a*number*of*challenges,*simple*null_hypothesis*significance*tests*and*p_values*have*

come*under*harsh*criticism*as*well*(Schmidt,*1992,*Schmidt*and*Hunter,*1997,*Cumming,*

2012,*2013,*Hupé,*2015).*The*meaning*and*relevance*of*null_hypothesis*significance*

testing*and*associated*statistics*(such*as*t*and*F*statistics)*has*become*so*hotly*contested*

that*some*journals*have*outright*banned*reporting*of*such*values*(Savalei*and*Dunn,*2015,*

Trafimow*and*Marks,*2015).**

Bearing*in*mind*these*considerations,*we*concluded*that*effect*sizes*are*worth*

calculating*and*reporting*in*meta_analyses*of*neuroimaging*data,*so*long*as*these*serious*

limitations*are*noted*and*attempts*are*made*to*correct*for*them.*The*many*relevant*issues*

are*discussed*at*length*in*the*Supplementary*Methods*section.*

Briefly,*our*procedure*for*applying*these*corrections*was*as*follows:*After*

calculating*effect*sizes*directly*from*the*peak*or*maximum*t!or!F!statistics!reported*in*the*

original*studies,*we*then*adjusted*these*values*downward*to*approximate*more*

conservative*estimates*of*t*or*F*statistics*for*the*entire*cluster*of*significant*difference.*

Next,*we*further*deflated*these*values*to*account*for*the*inflationary*bias*of*effect*sizes*

derived*only*from*results*that*have*exceeded*stringent*statistical*thresholds*(Schmidt,*

1992).*In*these*ways,*we*aimed*to*provide*effect*size*estimates*that*more*closely*

approximate*true*effect*sizes.*It*should*be*noted,*however,*that*we*neither*claim*nor*expect*

that*this*procedure*is*ideal.*It*is*clear*that*some*deflation*of*reported*values*is*necessary*

(Schmidt,*1992,*Yarkoni,*2009,*Yarkoni*et*al.,*2010,*Hupé,*2015),*but*the*best*method*and*

optimal*degree*of*deflation*remains*unclear.*As*such,*our*methods*are*a*preliminary*effort*

to*produce*effect*sizes*that*are*more*accurate*than*those*produced*by*calculations*solely*



based*on*t_statistics*reported*in*the*literature,*but*should*not*by*any*means*be*considered*

a*definitive*approach.*For*full*details,*as*well*as*specific*formulas*used,*see*the*

Supplementary*Methods.*

*

2.6!Estimating!publication!bias!in!meta8analytic!results!

+ The*bias*toward*publication*of*only*positive*(i.e.,*non_null)*results*is*a*serious*

concern*(the*‘file*drawer’*problem;*c.f.*(Rosenthal,*1979).*We*constructed*a*funnel*plot*

(scatterplot*of*effect*size*against*sample*size)*to*test*for*potential*publication*bias*in*our*

sample*of*studies*(Egger*et*al.,*1997).*Effect*sizes*were*calculated*as*described*above*and*

in*the*Supplementary*Methods,*and*plotted*against*total*sample*size*(meditators*+*

controls).*For*detailed*discussion*of*funnel*plots*see*Egger*and*colleagues*(1997).*For*other*

examples*of*their*use*in*meta_analyses*of*meditation*and*further*discussion*see*Fox*and*

colleagues*(2014)*and*Sedlmeier*and*colleagues*(2012).+

!

!



3.+Results+I:+Neuroimaging+meta?analysis+

+

3.1!Focused!attention!meditation!

* Meta_analysis*of*focused*attention*studies*resulted*in*2*significant*clusters*of*

activation,*both*in*prefrontal*cortex*(Table*3;*Fig.*2).*Activations*were*observed*in*regions*

associated*with*the*voluntary*regulation*of*thought*and*action,*including*the*premotor*

cortex*(BA*6;*Fig.*2e)*and*dorsal*anterior*cingulate*cortex*(BA*24;*Fig.*2a).*Slightly*sub_

threshold*clusters*were*also*observed*in*the*dorsolateral*prefrontal*cortex*(BA*8/9;*Fig.*

2c)*and*left*mid*insula*(BA*13;*Fig.*2e);*we*display*these*somewhat*sub_threshold*results*

here*because*of*the*obvious*interest*of*these*findings*in*practices*that*involve*top_down*

focusing*of*attention,*typically*focused*on*respiration.*We*also*observed*clusters*of*

deactivation*in*regions*associated*with*episodic*memory*and*conceptual*processing,*

including*the*ventral*posterior*cingulate*cortex*(BA*31;*Fig.*2d)*and*left*inferior*parietal*

lobule*(BA*39;*Fig.*2f).*A*detailed*series*of*slices*covering*the*entire*brain*is*presented*in*

Fig.*S1.*

* A*supplementary*meta_analysis,*excluding*studies*that*investigated*only*

practitioners*with*short_term*training,*yielded*nearly*identical*results*(see*Table*S2).*

*

**

! !



Table!3.*Activations*and*deactivations*associated*with*focused*attention*meditation**

Region+ Cluster+Size+(mm3)+

Side+ Peak+Coordinates++(x,+y,+z)+

Peak+ALE+value+

Activations+

Premotor*cortex* 712* L* _36,*6,*56*(BA*6)* 0.0144*

Dorsal*anterior/mid*cingulate*cortex* 280* M* 2,*12,*32*(BA*24)* 0.0112*

Deactivations+

Posterior*cingulate*cortex* 152* M* _6,*_60,*18*(BA*30)* 0.0071*

Inferior*parietal*lobule* 144* L* _48,*_72,*30*(BA*39)* 0.0071*

!!!Figure!2.!Peak*activations*and*deactivations*associated*with*focused*attention*meditation*!

**(a)*Dorsal*anterior/mid*cingulate*cortex*(b)*Premotor*cortex/posterior*dorsolateral*prefrontal*cortex.*(c)*Sub_threshold*cluster*in*dorsolateral*prefrontal*cortex.*(d)*Posterior*cingulate*cortex.*(e)*Sub_threshold*cluster*in*mid_insula.*(f)*Inferior*parietal*lobule.*Warm*colors:*activations;*cool*colors:*deactivations.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S1).*!

3.!2!Mantra!recitation!meditation!

! A*meta_analysis*of*mantra*recitation*studies*revealed*seven*significant*activation*

clusters*(Table*4).*Activations*were*observed*in*regions*associated*with*planning*and*



executing*voluntary*motor*output,*including*the*posterior*dorsolateral*prefrontal*

cortex/left*premotor*cortex*(BA*6/8;*Fig.*3d),*pre_supplementary*motor*cortex,*

supplementary*motor*cortex*(BA*6;*Fig.*3a),*and*putamen/lateral*globus*pallidus*(Fig.*3b).*

Other*activations*were*observed*in*regions*associated*with*visual*processing*and*mental*

imagery*including*the*fusiform*gyrus*(Fig.*3c),*cuneus*(BA*18),*and*precuneus*(BA*7)*(Fig.*

S2).*There*was*also*a*small*(but*non_significant)*cluster*located*within*Broca's*area*(BA*

44/6),*consistent*with*the*verbal*component*of*mantra*recitation.*A*single*cluster*of*

deactivation*was*observed*(Table*4)*in*the*left*anterior*insula*(BA*13)/claustrum*(Fig.*3b),*

a*region*associated*with*processing*viscero_somatic*body*signals.*A*detailed*series*of*slices*

covering*the*entire*brain*is*presented*in*Fig.*S2.*


practitioners*with*short_term*training,*yielded*nearly*identical*results.*The*only*notable*

difference*was*the*disappearance*of*the*single*deactivation*cluster*in*the*anterior*insula*

(see*Table*S3).*Although*ALE*implements*controls*for*sample*size,*another*concern*was*the*

inclusion*of*two*studies*with*very*small*sample*sizes*–*Lazar*et*al.*(2000)*with*n*=*5,*and*

Davanger*et*al.*(2010)*with*n*=*4*–*which*might*still*have*unduly*influenced*the*results.*We*

therefore*also*executed*our*analysis*with*data*from*these*two*studies*excluded.*This*had*

no*effect*on*the*pattern*of*deactivations.*All*remaining*clusters*of*activation*were*the*same,*

but*two*clusters*disappeared*from*the*results:*the*putamen/lateral*globus*pallidus,*and*the*

small*(112*mm3)*cluster*in*the*supplementary*motor*area.*

!

!

!

!



Table!4.*Activations*and*deactivations*associated*with*mantra*recitation*meditation*



Peak+ALE+value+

Activations+

Premotor*cortex* 896* L* _30,4,*60*(BA*6)* 0.0137*

Supplementary*motor*area*584* M* 0,*12,*54*(BA*6)* 0.0111*

112* M* _4,*2,*68*(BA*6)* 0.0080*

Putamen/Lateral*globus*pallidus* 368* R* 28,*_16,*_6* 0.0111*

Fusiform*gyrus* 248* R* 40,*_26,*_30*(BA*20/36)* 0.0093*

Cuneus* 160* R* 24,*_86,*26*(BA*18)* 0.0082*

Precuneus* 152* L* _14,*_56,*54*(BA*7)* 0.0082*

Deactivations+

Anterior*insula* 192* L* _28,*25,*_7*(BA*13)* 0.0075*

!!Figure!3.!Peak*activations*and*deactivations*associated*with*mantra*recitation*meditation*!

!

(a)*Supplementary*motor*area.*(b)*Bilateral*deactivations*in*the*anterior*insula*(blue)*and*activations*in*the*right*basal*ganglia*(putamen*and*globus*pallidus).*(c)*Fusiform*gyrus.*(d)*Premotor*cortex.*Warm*colors:*activations;*cool*colors:*deactivations.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S2).*



3.3!Open!monitoring!meditation!

! Meta_analysis*of*open*monitoring*studies*showed*five*significant*clusters*of*

activation*(Table*5).*One*cluster*was*located*in*the*insula*(BA*13;*Fig.*4d),*consistent*with*

awareness*of*ongoing*viscero_somatic*body*signals.*Other*significant*clusters*were*

observed*in*regions*associated*with*the*voluntary*control*of*action,*including*the*left*

inferior*frontal*gyrus*(BA*44/45;*Fig.*4b),*pre_supplementary*motor*area*(BA*32/6;*Fig.*

4a),*supplementary*motor*area*(BA*6;*Fig.*4a,c),*and*premotor*cortex*(BA*6;*Fig.*4*c).*

Smaller*(non_significant)*clusters*were*observed*in*the*rostrolateral*prefrontal*cortex*(BA*

10)*and*mid_dorsolateral*prefrontal*cortex*(BA*9/46)*―*regions*associated*with*cognitive*

control*and*metacognitive*awareness.*We*observed*a*single*significant*cluster*of*

deactivation*(Table*5)*in*the*right*thalamus*(Fig.*4d).*A*detailed*series*of*slices*covering*the*

entire*brain*is*presented*in*Fig.*S3.*


practitioners*with*short_term*training,*yielded*similar*results*(Table*S4).*Some*of*the*more*

salient*differences*are*outlined*in*the*Discussion,*below*(also,*compare*Table*5*with*Table*

S4).*

*

! !



Table!5.*Activations*and*deactivations*associated*with*open*monitoring*meditation**



Peak+ALE+value+

Activations+

Supplementary*motor*area* 824* M* _6,*4,*60*(BA*6)* 0.0165*

Dorsal*anterior*cingulate*cortex/*pre_supplementary*motor*area* 368* M* _6,*18,*44*(BA*32/6)* 0.0110*

Insular*cortex*(mid/anterior)* 360* L* _44,*10,*4*(BA*13)* 0.0111*

Inferior*frontal*gyrus* 200* L* _50,*16,*14*(BA*44/45)* 0.0092*


Deactivations*

Thalamus*(pulvinar)* 112* R* 17,*_24,*11* 0.0084*

!

Figure!4.*Peak*activations*and*deactivations*associated*with*open*monitoring*meditation+

+

(a)*Supplementary*motor*area*(larger,*more*superior*cluster)*and*dorsal*anterior*cingulate*cortex/pre_supplementary*motor*area.*(b)*Inferior*frontal*gyrus.*(c)*Premotor*cortex*(smaller*cluster*to*left),*and*supplementary*motor*area*also*visible*again*(center).*(d)*Activation*in*mid/anterior*insula*and*bilateral*deactivations*in*the*thalamus.*Warm*colors:*activations;*cool*colors:*deactivations.*L:*left;*R:*right.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S3).*!



3.4!Loving8kindness!and!compassion!meditation*

Meta_analysis*of*loving_kindness*and*compassion*meditation*revealed*significant*

activation*clusters*in*3*regions*(Table*6).*Activations*were*observed*in*regions*associated*

with*awareness*of*bodily*sensations*and*feelings*including*the*right*anterior*insula/frontal*

operculum*(BA*13;*Fig.*5a)*and*secondary*somatosensory*areas*extending*into*the*anterior*

inferior*parietal*lobule*(BA*2/40;*Fig.*5b).*Additionally,*activation*was*observed*near*the*

parieto_occipital*sulcus*(BA*23/31;*Fig.*5c).*No*significant*deactivations*were*observed.*A*

detailed*series*of*slices*covering*the*entire*brain*is*presented*in*Fig.*S4.*

A*supplementary*meta_analysis,*excluding*studies*that*investigated*only*

practitioners*with*short_term*training,*yielded*nearly*identical*results.*The*only*significant*

difference*was*the*appearance*of*a*small*cluster*of*activation*in*the*left*somatosensory*

cortices*(see*Table*S5).*

!

! !



Table!6.*Activations*and*deactivations*associated*with*loving_kindness*and*compassion*

meditation*



Peak+ALE+value+

Activations+

Anterior*insula* 512* R* 38,*22,*14*(BA*13)* 0.0135*

Parieto_occipital*sulcus* 344* R* 24,*_60,*18*(BA*23/31)* 0.0115*

Somatosensory*cortices/Inferior*parietal*lobule*

320* R* 54,*_26,*30*(BA*2/40)* 0.0101*

!!

Figure!5.!!!Peak*activations*associated*with*loving_kindness*and*compassion*meditation!

!

(a)*Right*anterior*insula/frontal*operculum.*(b)*Right*somatosensory*cortices.*(c)*Parieto_occipital*sulcus.*L:*left;*R:*right.*See*the*supplementary*materials*for*a*detailed*series*of*slices*covering*the*entire*brain*(Fig.*S4).*!

+ +



4.+Results+II:+Effect+size+meta?analysis++

+ As*detailed*in*the*Supplementary*Methods,*we*derived*effect*sizes*(Cohen’s*d)*from*

studies*that*reported*t*or*F*statistics,*and*then*adjusted*these*raw*effect*sizes*for*the*severe*

inflationary*bias*that*influences*effect*sizes*in*all*neuroimaging*research.*From*our*

adjusted*effect*sizes*for*each*individual*reported*result,*we*then*calculated*mean*positive*

(+)*and*negative*(–)*effect*sizes*for*each*study*(and*for*each*different*practice*within*a*

study,*if*more*than*one*was*examined).*These*results*are*reported*in*Table*7.*We*then*

pooled*these*data*to*calculate*mean*(+)*and*(–)*effect*sizes*for*each*type*of*practice*(Table*

8).*Recall*that*in*total,*two*deflation*coefficients*were*employed*to*adjust*for*suspected*

inflation*bias.*Coefficients*of*0.697*and*0.60,*for*a*net*coefficient*of*0.4182,*were*applied*to*

the*effects*calculated*from*the*primary*reports.*Therefore,*in*order*to*obtain*the*

unadjusted*values,*simply*multiply*our*effect*size*results*by*2.391.*For*details*see*Methods*

section*2.5.*

+

! !



Table!7.***Summary*of*adjusted*mean*effect*sizes*for*each*study*and*practice*type.!

Study+ Sample+(N)+ Practice+Mean+(+)+effect+size+

(Cohen’s+d)+Mean+(–)+effect+size+

(Cohen’s+d)+

Brefczynski_Lewis*et*al.*(2007)* 30* FA* 0.51* –*

Lutz*et*al.*(2008)* 32* LK* 0.33* –*

Lutz*et*al.*(2009)* 22* LK* 0.56* –*

Davanger*et*al.*(2010)* 4* MR* 1.48* –*

Manna*et*al.*(2010)* 8*FA* 1.56* _1.29*

OM* 1.25* –*

Brewer*et*al.*(2011)* 25*

FA* –* _0.71*

OM* –* _0.58*

LK* –* _0.68*

Gard*et*al.*(2011)* 34* OM* 0.46* –*

Ives_Deliperi*et*al.*(2011)* 10* OM* 2.03* _2.01*

Kalyani*et*al.*(2011)* 12* MR* –* _1.11*

Taylor*et*al.*(2011)* 22* OM* –* _0.79*

Dickenson*et*al.*(2012)* 31* FA* 0.49* –*

Hasenkamp*et*al.*(2012)* 14* FA* 0.67* –*

Lee*et*al.*(2012)* 44*FA* 0.56* –*

LK* 0.54* –*

Farb*et*al.*(2013)* 36* OM* 0.71* –*

Lutz*et*al.*(2013)* 28* OM* 0.58* _0.62*

Weng*et*al.*(2013)* 41* LK* 0.36* –*

Lutz*et*al.*(2014)* 46* OM* 0.51* _0.45*

++! !



Table!8.*Summary*of*adjusted*mean*effect*sizes*by*meditation*practice*type!

Meditation+Type+Contributing+Experiments+

(N)+

Mean+(+)+effect+size+(Cohen’s+d)a+

Mean+(–)+effect+size+(Cohen’s+d)a+

Focused*attention* 6* 0.60!±*0.05* _0.85*±*0.09*Mantra*recitation* 2* 1.48* _1.11*

Open*monitoring* 8* 0.68*±*0.12* _0.69*±*0.14*Loving_kindness/compassion* 5* 0.44*±*0.01* _0.68*

All+practices+combined+ 21+ M+=+0.59+±+0.02+ M+=+?0.74!±+0.09+Mean*effect*sizes*±!95%*confidence*intervals.*Note*that*the*‘mean’*effect*sizes*for*mantra*recitation*are*based*on*only*a*single*study*each,*as*are*negative*effect*sizes*for*loving_kindness/compassion*meditations*(cf.*Table*7).*Accordingly,*no*confidence*intervals*are*provided*since*there*was*no*variance*in*the*estimates.*Note*that*a*total*of*21*‘experiments’*were*analyzed,*from*17*independent*studies*of*the*25*studies*originally*included*in*the*neuroimaging*meta_analysis.*The*remaining*studies*did*not*provide*statistical*data*that*allowed*for*calculation*of*Cohen’s*d.**++Figure!6.*Funnel*plot*showing*weighted*means*of*both*negative*and*positive*effect*sizes**

+The*two*anchor*lines*represent*the*means*for*all*(–)*and*(+)*effect*sizes*(_0.74*and*+0.59,*respectively)*weighted*by*sample*size.*Positive*effect*sizes*relate*to*brain*activations*during*meditation,*whereas*negative*effect*sizes*represent*brain*deactivations.*See*Tables*7*and*8*for*details.*+



5.+Discussion,+future+directions,+and+conclusions+

+

5.1!Overview!

* The*ensuing*discussion*is*divided*into*three*broad*sections:**

(i)*First,*we*outline*and*interpret*the*various*results*from*our*meta_analysis*and*

qualitative*review*of*neuroimaging*findings*(sections*5.2_5.8).*We*synthesize*and*simplify*

all*of*these*results*in*a*single*summary*figure*(Fig.*7).*We*focus*on*the*clusters*that*

attained*statistical*significance*in*our*meta_analysis,*but*it*should*be*recalled*that*

significance*and*cluster*thresholds*are*ultimately*arbitrary*and*should*not*restrict*

discussion.*Some*‘significant’*clusters*are*difficult*to*understand*or*explain,*whereas*some*

non_significant*clusters*dovetail*extremely*well*with*the*stated*techniques*and*goals*of*a*

given*form*of*meditation.*We*therefore*endeavor*to*offer*as*integrated*and*impartial*a*

discussion*as*possible,*including*consideration*of*meta_analytic*activations*that*may*not*

have*exceeded*our*cluster*thresholds.*We*also*integrate*the*limited*findings*from*the*three*

meditation*categories*that*could*not*be*included*in*the*quantitative*meta_analysis,*for*the*

same*reasons:*preliminary*data,*even*if*tentative,*is*still*informative*and*relevant*to*our*

discussion.*In*a*similar*vein,*the*figures*in*our*Results*section,*for*the*sake*of*clarity,*focus*

on*the*most*reliable,*consistent*clusters*for*each*category*of*meditation.*However,*we*have*

presented*detailed*series*of*slices*in*our*supplementary*materials*in*order*to*clearly*

visualize*all*activations*associated*with*a*given*meditation*type*(not*just*those*that*

exceeded*our*cluster*and*significance*thresholds;*see*Figs.*S1_S4).*



(ii)*Second,*we*discuss*the*results*of*our*effect*size*meta_analysis*(section*5.9),*and*

its*implications*for*the*‘practical*significance’*of*the*functional*neural*effects*associated*

with*meditation.*We*also*discuss*the*possibility*of*publication*bias.**

(iii)*Finally,*several*sections*(5.10_5.13)*outline*the*limitations*of*our*meta_analysis,*

the*relevance*of*these*results*to*clinical*conditions,*and*the*implications*for*future*avenues*

of*research.*

*

Figure!7.*Simplified*summary*of*all*meta_analytic*activations*and*deactivations.!!

Filled*circles*indicate*activations;*circles*with*downward*arrows*indicate*deactivations.*All*labels*are*approximate*and*intended*for*illustrative*purposes*only.*Medial*meta_analytic*clusters*are*arbitrarily*represented*on*a*right*hemisphere*view*merely*for*simplicity;*lateral*and*insular*clusters*are*represented*in*the*correct*hemisphere.*For*the*specific*location*of*each*cluster,*see*Tables*3_6*and*Supplementary*Figures*1_4.** **

!

!



5.2!Functional!neuroanatomy!of!focused!attention!meditation!

+ 5.2.1+Activations.+Focused*attention*meditation*was*associated*with*activations*in*

regions*associated*with*cognitive*control*and*self_reflection.*Directly*in*line*with*others’*

predictions*(Lutz*et*al.,*2008b),*we*found*activations*in*the*premotor*cortex*extending*into*

the*posterior*dorsolateral*prefrontal*cortex,*as*well*as*in*the*dorsal*anterior*cingulate*

cortex.*We*also*observed*a*slightly*sub_threshold*(88*m3)*cluster*in*the*dorsolateral*

prefrontal*cortex*(BA*8/9).*These*regions*are*frequently*activated*in*studies*of*cognitive*

control*that*require*monitoring*performance,*and*the*voluntary*regulation*of*attention*and*

behavior,*such*that*task_relevant*actions*are*selected*(Carter*et*al.,*1998,*Vincent*et*al.,*

2008,*Dixon*and*Christoff,*2012,*Dixon*et*al.,*2014a).*The*recruitment*of*such*executive*

brain*areas*is*consistent*with*a*contemplative*practice*consisting*largely*of*effortful,*

sustained*attention*with*a*range*of*regulation*demands.*For*more*details,*see*the*

Supplementary*Discussion.* *

5.2.2+Deactivations.+Consistent*deactivations*were*observed*in*two*major*hubs*of*

the*default*mode*network:*the*posterior*cingulate*cortex*(BA*23/31)*and*the*posterior*

inferior*parietal*lobule*(BA*39)*(Buckner*et*al.,*2008).*These*regions*have*well_established*

roles*in*mind_wandering*(Fox*et*al.,*2015),*and*in*particular,*episodic*memory*retrieval,*

simulation*of*future*events,*and*conceptual/semantic*processing.*Deactivations*in*these*

regions*suggest*that*focused*attention*meditation*may*diminish*spontaneous*thoughts*

regarding*past*and*future*events,*as*well*as*their*conceptual*elaboration.*Although*many*

regions*beyond*the*default*mode*network*are*implicated*in*mind_wandering*and*related*

spontaneous*thought*processes,*the*default*mode*network*nonetheless*plays*an*essential*

role*(Fox*et*al.,*2015).*For*more*details,*see*the*Supplementary*Discussion.*



5.3!Functional!neuroanatomy!of!mantra!recitation!meditation!

! 5.3.1+Activations.+The*most*salient*activations*for*mantra*recitation*meditation*

were*in*the*motor*control*network,*including*Broca's*area,*the*premotor*and*

supplementary*motor*cortices*(lateral*and*medial*BA*6),*as*well*as*the*putamen*within*the*

basal*ganglia.*Consistent*with*the*goals*of*mantra*meditation,*these*regions*may*be*

involved*in*the*process*of*internally*generating*and*staying*focused*on*a*phrase*within*

one's*mind*(or*recited*aloud).+

* Particularly*interesting*was*a*small*cluster*in*Broca’s*area*(BA*44),*extending*

posteriorly*into*the*face/tongue*area*of*premotor*cortex*(BA*6).*This*area*is*well_known*

from*the*neuropsychological*lesion*work*of*Pierre*Paul*Broca*to*be*critically*involved*in*

the*motor*components*of*speech*production*(Broca,*1861).*Its*consistent*recruitment*

during*mantra*recitation*requires*little*comment.*

* Large*activations*were*also*observed*in*various*areas*of*the*basal*ganglia,*including*

bilateral*clusters*in*both*the*putamen*and*globus*pallidus.*Although*these*areas*play*a*clear*

role*in*‘reward’*(Schultz*et*al.,*2000),*they*are*most*strongly*implicated*in*highly_practiced*

motor*movements*and*habit*formation*in*general*(Yin*and*Knowlton,*2006,*Ashby*et*al.,*

2010).*In*a*broader*sense,*the*basal*ganglia*are*thought*to*aid*in*the*inhibition*of*undesired*

movements,*and*in*facilitating*the*smooth*execution*of*those*movements*that*are*desired,*

via*tight*reciprocal*connections*with*premotor*areas*(Chakravarthy*et*al.,*2010,*Stocco*et*

al.,*2010).*These*latter*functions*are*all*consistent*with*a*meditation*practice*that*primarily*

involves*the*deliberate*execution*of*a*highly_practiced*and*highly_specific*sequence*of*

motor*behavior*(whether*imagined*in*detail*or*recited*aloud).*For*more*details,*see*the*

Supplementary*Discussion.* *



5.3.2+Deactivations.+An*interesting*pattern*of*deactivations*was*observed,*

suggesting*decreased*processing*of*external*sensory*(particularly*somatosensory)*inputs.*

Deactivations*were*observed*bilaterally*in*the*anterior*insula,*and*at*a*sub_threshold*level*

in*the*thalamus,*left*primary*somatosensory*cortex*(postcentral*gyrus;*BA*2),*and*left*

inferior*parietal*lobule*(BA*40).*All*of*these*areas*are*centrally*involved*in*processing*and*

awareness*of*somatosensory*and*interoceptive*information*(Penfield*and*Boldrey,*1937,*

Bonda*et*al.,*1995,*Craig,*2004,*2009).*Deactivations*were*also*observed*in*primary*

auditory*cortex*(BA*41)*and*in*the*posterior*area*of*the*superior*temporal*gyrus*(BA*22),*

both*well_known*to*be*involved*in*the*processing*and*comprehension*of*sounds*and*

language*(Galaburda*and*Sanides,*1980,*Demonet*et*al.,*1992).*

One*of*the*reasons*mantra*is*employed*is*to*heighten*the*effectiveness*of*focused*

attention*meditation.*The*implication*is*that*by*focusing*upon*a*single*salient*percept*(the*

mantra),*attention*is*more*easily*sustained*and*distractors*more*easily*ignored*than*

without*the*mantra*(Goenka,*2000).*The*observed*pattern*of*deactivations*is*consistent*

with*the*idea*that*mantra*aids*in*maintaining*a*sharp*focus*of*attention,*to*the*exclusion*of*

incoming*sensory*stimuli*and*awareness*of*one’s*own*body.*Deactivations*in*auditory*and*

language_comprehension*areas*are*also*intriguing*in*that*the*mantra*is*intended*as*a*tool*

for*focusing*attention,*but*is*not*usually*meant*to*be*understood*semantically.*!

5.4!Functional!neuroanatomy!of!open!monitoring!meditation!

* 5.4.1+Activations.+Open*monitoring*meditation*was*associated*with*activation*in*

regions*involved*in*the*voluntary*regulation*of*thought*and*action*(inferior*frontal*gyrus,*

posterior*dorsolateral*prefrontal*cortex/pre_motor*cortex,*and*dorsal*anterior*cingulate*

cortex/pre_supplementary*motor*area),*as*well*as*activation*in*the*insula,*a*region*that*



plays*a*key*role*in*interoceptive*processing.*As*all*of*these*areas*were*recruited*by*multiple*

meditation*techniques,*they*are*discussed*in*more*detail*below*in*Section*5.6*on*

‘Convergent*findings.’*

* Smaller*clusters*that*did*not*exceed*our*threshold+were*observed*in*left*

rostrolateral*prefrontal*cortex*(BA*10)*and*left*mid_dorsolateral*prefrontal*cortex*(BA*

9/46).*Together*with*the*dorsal*anterior*cingulate*cortex,*these*areas*constitute*key*parts*

of*a*‘frontoparietal*control’*network*(Vincent*et*al.,*2008,*Spreng*et*al.,*2010)*generally*

involved*in*cognitive*control,*that*is,*coordinating*and*monitoring*attention*to*both*

internal*and*external*channels*of*information*(Spreng,*2012,*Dixon*et*al.,*2014b).*Given*

that*open*monitoring*meditation*typically*involves*a*broad,*non_judgmental*attention*to*

any*and*all*mental*content*(including*information*from*the*outside*world,*from*within*the*

body,*and*also*internal*channels*of*thought*and*memories),*it*is*congruous*that*this*

practice*recruits*numerous*areas*from*the*frontoparietal*control*network.**

5.4.2+Deactivations.+Only*a*single*significant*deactivation*was*observed,*in*the*

right*thalamus,*and*a*sizeable*(albeit*sub_threshold)*deactivation*was*also*observed*in*the*

left*thalamus.*Interestingly,*in*the*supplemental*meta_analysis*(which*excluded*

practitioners*with*only*brief*training*in*this*practice),*these*findings*were*even*more*

salient*(Table*S5).*The*thalamus*is*the*key*relay*center*for*most*incoming*sensory*

information,*and*also*functions*in*‘sensory*gating’*(i.e.,*the*selective*filtering*out*of*certain*

sensory*signals).*Interestingly,*increased*intensity*of*sensory*gating*appears*to*be*

correlated*with*increased*activity*in*the*thalamus*(LaBerge,*1990,*LaBerge*and*Buchsbaum,*

1990,*Banich,*2004).*Therefore,*deactivations*here*suggest*decreased*sensory*gating,*an*



interpretation*that*aligns*well*with*the*goal*of*being*open*and*receptive*to*sensory*stimuli.*

For*more*details,*see*the*Supplementary*Discussion.* *

!

5.5!Functional!neuroanatomy!of!loving8kindness!and!compassion!meditation!

5.5.1+Activations.+Loving_kindness*and*compassion*meditation*involve*cultivating*

positive*emotions,*such*as*joy*and*compassion,*as*well*as*prosocial*skills*and*tendencies,*

such*as*empathic*concern*and*altruistic*behavior.*They*focus*on*active*‘mentalizing’*in*the*

form*of*taking*the*perspective*of*others*and*imagining*their*emotional*experiences.*

Mounting*evidence*from*behavioral*studies*suggests*that*these*practices*can*be*effective,*

and*that*even*brief*training*in*compassion*meditation*can*increase*empathy*for,*and*

prosocial*behavior*toward,*others*(Leiberg*et*al.,*2011,*Condon*et*al.,*2013,*Kang*et*al.,*

2013,*Weng*et*al.,*2013,*Lim*et*al.,*2015).*One*study*even*found*that*compassion*

meditation_driven*changes*in*brain*activation*specifically*predicted*subsequent*

compassionate*behavior*toward*an*unknown*victim*(Weng*et*al.,*2013).**

Only*three*significant*meta_analytic*clusters*were*observed,*probably*due*to*the*low*

power*of*this*analysis,*which*involved*the*fewest*studies*(N*=*5*experiments;*see*Table*1).*

One*large*cluster*was*observed*in*the*right*somatosensory*cortices*(BA*2),*extending*into*

the*inferior*parietal*lobule*(BA*40).*A*similarly*located*(albeit*statistically*non_significant)*

cluster*was*observed*on*the*postcentral*gyrus*of*the*left*hemisphere,*centered*on*BA*43*

and*extending*into*BA*3.*These*parts*of*parietal*lobe*play*a*well_known*role*in*

somatosensory*processing*and*in*creating*a*unified*sense*of*the*body*(Penfield*and*

Boldrey,*1937,*Penfield*and*Rasmussen,*1950),+but*both*regions*have*also*been*implicated*

in*empathy*in*a*recent*meta_analysis*(Lamm*et*al.,*2011)*and*comprehensive*review*



(Bernhardt*and*Singer,*2012).*Both*areas*are*also*consistently*implicated*in*the*perception*

of*pain*(Grant*et*al.,*2011,*Grant,*2014),*but*this*function*may*overlap*with*their*role*in*

empathy,*as*part*of*the*proposed*role*of*these*areas*in*empathy*may*be*in*specifically*

empathizing*with*the*pain*of*others*(Lamm*et*al.,*2011).*

Another*large*cluster*centered*on*the*right*anterior*insula,*which*has*previously*

been*implicated*in*quantitative*meta_analyses*(Lamm*et*al.,*2011)+of*the*neural*correlates*

of*empathy*and*theory_of_mind*(i.e.,*mentalizing).*Because*insula*activation*was*observed*

across*multiple*meditation*categories,*its*possible*role(s)*in*loving_kindness*meditation*is*

discussed*further*in*the*section*on*convergent*findings*(section*5.6).*For*more*details,*see*

the*Supplementary*Discussion.*

! 5.5.2+Deactivations.+No*significant*deactivations*were*observed;*for*more*details,*

see*the*Supplementary*Discussion.*!

)

5.6!Convergent!findings!across!meditation!categories!

* Relatively*few*regions*showed*significant*clusters*across*multiple*meditation*

categories,*supporting*the*central*hypothesis*of*this*paper*that*distinct*meditation*styles*

recruit*largely*non_overlapping*neural*networks.*Only*a*single*area*(insular*cortex)*was*

recruited*by*all!four*meditation*categories.*Some*additional*consistencies*across*

meditation*types*were*observed,*however;*each*area*is*considered*in*turn*below.*

5.6.1+Insular+cortex.*Meta_analytic*activations*were*observed*in*insular*cortex*in*

all*four*meditation*categories*explored*here.*For*focused*attention,*a*small*(non_

significant)*cluster*was*observed*in*the*left*anterior*insula,*as*well*as*a*somewhat*larger*

(also*non_significant)*cluster*in*the*left*mid_insula.*For*mantra*recitation,*a*very*small*



(non_significant)*cluster*was*observed*in*the*left*mid_insula/claustrum.*For*open*

monitoring*meditation,*a*large*(significant)*cluster*was*observed*in*the*left*anterior/mid_

insula,*as*well*as*two*smaller*(non_significant)*clusters*in*the*right*mid_*and*posterior*

insula.*For*loving_kindness*meditation,*a*large*(significant)*cluster*was*observed*in*the*

right*anterior*insula.*The*insula*therefore*appears*to*be*reliably*recruited*in*two*categories*

of*meditation*we*examined,*and*shows*evidence*for*recruitment*in*the*two*other*styles.*

* These*findings*suggest*an*important*role*for*the*insula*across*numerous*meditative*

practices.*They*are*also*consistent*with*our*recent*meta_analysis*of*morphometric*

neuroimaging*of*meditation,*which*collapsed*across*many*meditation*styles*and*found*that*

differences*in*insula*were*the*most*consistent*structural*alterations*(Fox*et*al.,*2014).*

Although*the*insula*has*many*roles,*probably*the*most*consistently*replicated*and*

thoroughly*investigated*is*its*involvement*in*interoception*(i.e.,*monitoring*and*conscious*

awareness*of*internal*body*states,*such*as*respiration*or*heart*rate)*(Craig,*2004,*Critchley*

et*al.,*2004,*Craig,*2009,*Farb*et*al.,*2013)*as*well*as*empathy*(Lamm*et*al.,*2011)*and*

possibly*even*metacognition*(Fleming*and*Dolan,*2012).*Given*that*virtually*all*forms*of*

meditation*investigated*here*involve*some*degree*of*monitoring*of*the*body,*some*

awareness*of*respiration,*and*basic*metacognitive*monitoring,*universal*recruitment*of*

insular*cortex*is*not*unreasonable.**

* Insular*cortex*is*not*functionally*homogenous,*however:*there*is*evidence*that*the*

mid*and*posterior*insula*serve*as*‘primary’*interoceptive*cortex,*receiving*and*processing*

direct*interoceptive*inputs*from*the*thalamus*(Flynn,*1999,*Hua*et*al.,*2005,*Frot*et*al.,*

2007),*whereas*more*anterior*parts*of*the*insula*are*preferentially*involved*in*conscious*

awareness*of*interoceptive*signals*and*the*integration*of*this*information*with*one’s*



higher_order*goals*and*emotional*states*(Craig,*2004,*Critchley*et*al.,*2004,*Critchley,*2005,*

Craig,*2009).*In*this*light*it*is*interesting*that*anterior*insula*was*recruited*in*all*techniques*

except*mantra*recitation*–*which*is*the*technique*least*focused*on*conscious*awareness*of*

the*body,*and*most*geared*toward*detaching*from*immediate*sensory*stimuli.*This*

interpretation*is*speculative,*of*course;*

for*more*details,*see*the*Supplementary*Discussion.* *

5.6.2+Premotor+cortex+and+supplementary+motor+area+(lateral/medial+BA+6).***

Three*categories*of*meditation*(the*exception*being*loving_kindness/compassion)*showed*

large*meta_analytic*clusters*in*posterior*dorsolateral*prefrontal*cortex/premotor*and*

supplementary*motor*cortices*(BA*6).*Although*these*areas*are*traditionally*considered*

‘motor’*regions,*a*wealth*of*recent*work*has*demonstrated*that*they*also*play*a*role*in*

many*cognitive*functions*(e.g.,*(Hanakawa*et*al.,*2002,*Tanaka*et*al.,*2005).*Specifically,*it*

has*been*proposed*that*these*areas*could*play*a*role*analogous*to*their*motor*function*of*

manipulating*objects*in*the*physical*world*–*namely,*the*mental*manipulation*of*

psychological*content*and*memory*(Hanakawa*et*al.,*2002).*Functional*neuroimaging*

studies*have*shown*activation*in*these*areas*during*a*variety*of*complex*mental*tasks,*

including*working*memory*(Fiez*et*al.,*1996,*Owen*and*Evans,*1996),*attentional*control*

(Hopfinger*et*al.,*2000,*Boussaoud,*2001),*mental*imagery*(Mellet*et*al.,*1996),*and*

conceptual*reasoning*(Rao*et*al.,*1997).*Given*the*apparent*role*of*these*regions*in*diverse*

higher_order*cognitive*functions*and*attention*regulation*–*the*core*of*all*meditation*

techniques*–*their*recruitment*across*numerous*styles*of*meditation*appears*reasonable.*

Speculatively,*then,*these*regions*may*interact*with*other*brain*areas*more*specifically*tied*



to*particular*meditation*techniques,*assisting*in*the*intentional*regulation*of*attention*and*

other*cognitive*processes*specific*to*the*practice*at*hand.***

5.6.3+Dorsal+anterior/mid+cingulate+cortex.*In*focused*attention*and*open*

monitoring*meditation,*we*observed*significant*activation*clusters*that*bordered*both*the*

supplementary*motor*areas*(discussed*in*the*previous*section)*and*the*dorsal*anterior*

cingulate*cortex.*Congruent*with*these*findings,*consistent*structural*alterations*in*dorsal*

anterior*cingulate*cortex*were*observed*in*our*recent*meta_analysis*of*morphometric*

neuroimaging*of*meditation*(Fox*et*al.,*2014).*Despite*numerous*functional*roles,*the*

dorsal*anterior*cingulate*is*clearly*a*key*player*in*the*brain’s*ability*to*regulate*attention*

and*emotion,*as*well*as*monitor*performance*(Bush*et*al.,*2000,*Posner*et*al.,*2007).*

Activations*here*across*the*two*styles*of*meditation*that*most*explicitly*involve*such*

regulation*and*monitoring*is*therefore*sensible.*For*further*discussion,*see*the*individual*

sections*on*focused*attention*and*open*monitoring.*

5.6.4+Frontopolar+cortex/rostrolateral+prefrontal+cortex.+We*observed*a*fairly*

large*but*sub_threshold*cluster*of*activation*in*the*left*frontopolar*cortex*(BA*10)*for*open*

monitoring*meditation.*For*loving_kindness/compassion*meditation,*we*observed*a*small*

(non_significant)*cluster*in*the*superior*portion*of*left*frontopolar*cortex*(BA*10),*

extending*somewhat*into*the*dorsolateral*prefrontal*cortex*(BA*9).*Although*neither*of*

these*results*exceeded*our*stringent*significance*thresholds,*nonetheless*these*findings*are*

in*line*with*our*recent*meta_analysis*of*morphometric*(i.e.,*structural_anatomical)*

neuroimaging*studies*of*meditation*(Fox*et*al.,*2014),*and*therefore*warrant*a*brief*

discussion.**



In*our*morphometric*meta_analysis,*we*reported*anatomical*increases*(e.g.,*

increased*cortical*thickness;*Lazar*et*al.,*2005)*in*this*area*across*three*fairly*divergent*

schools*of*practice*(Fox*et*al.,*2014).*This*region*is*known*to*play*a*key*role*in*meta_

awareness*and*metacognitive*capacity*generally*(e.g.,*(Fleming*et*al.,*2010,*McCaig*et*al.,*

2011,*Fleming*and*Dolan,*2012,*Fleming*et*al.,*2012,*Fox*and*Christoff,*2015)),*but*it*also*

appears*to*be*involved*in*the*evaluation*of*self_generated*information*(Christoff*et*al.,*

2003)*and*in*the*processing*of*complex*and*abstract*information*generally*(Christoff*et*al.,*

2001,*Christoff*et*al.,*2009).*Frontopolar*cortex*is*also*a*key*node*of*the*frontoparietal*

control*network*(Vincent*et*al.,*2008)*and*may*play*an*important*role*in*switching*

attention*between*external*and*internal*channels*(Ramnani*and*Owen,*2004,*Burgess*et*al.,*

2007).*The*specific*functions*of*the*frontopolar*cortex*in*various*forms*of*meditation*

remain*an*open*question.**

+

5.7!Other!meditation!practices:!Further!evidence!for!dissociability!at!the!neural!level!

* In*the*Introduction,*we*noted*that*there*are*several*other*major*categories*of*

meditation*wherein*research*remains*too*sparse*for*inclusion*in*a*meta_analysis*(Section*

1.3).*These*categories*include*visualization!(generating*and*sustaining*complex*visual*

imagery),!non8dual!awareness!(eroding*the*boundary*between*subject*and*object),!and!

pratyahara!(dampening*of*sensory*inputs).*Neural*correlates*of*these*practices*have*been*

reported*in*isolated*studies,*and*interestingly,*provide*further*support*for*the*hypothesis*

that*distinct*psychological*(Ψ)*practices*are*likewise*dissociable*at*the*neurobiological*(Φ)*

level*(Cacioppo*and*Tassinary,*1990).**



For*instance,*a*single*study*has*examined*the*neural*correlates*of*visualization*

meditation*(Lou*et*al.,*1999).*In*this*study,*practitioners*were*guided*through*“visual*

imagination*of*a*summer*landscape*with*forests,*streams,*and*meadows*with*cattle”*(Lou*

et*al.,*1999;*p.*100).*Although*this*particular*imagined*content*is*not*typical*of*visualization*

meditation*practices*(which*tend*to*focus*on*more*explicitly*religious*themes),*nonetheless*

the*results*are*telling.*Visualization*meditation*resulted*in*significant*recruitment*(among*

other*areas)*of*the*fusiform*gyrus*(definitively*linked*to*higher_order*visual*processing;*

(McCarthy*et*al.,*1997,*McCandliss*et*al.,*2003),*the*parahippocampal*gyrus*(linked*to*

visual*‘place’*perception;*(Epstein*et*al.,*1999),*and*nearly*universal*recruitment*of*medial*

and*lateral*occipital*areas*(Lou*et*al.,*1999).*Intriguingly,*primary*visual*cortex*(V1),*which*

is*not*required*for*the*creation*of*visual*imagery*and*visual*dreaming*(Solms,*1997),*was*

essentially*the*only*occipital*area*not*strongly*recruited*(Lou*et*al.,*1999).*These*results,*

although*drawn*from*only*a*single*study,*support*the*idea*that*practitioners*were*

successfully*engaging*in*such*a*visualization*practice.*More*importantly,*for*our*purposes,*

they*are*utterly*distinct*from*any*of*the*broad*patterns*of*neural*activity*reported*in*this*

meta_analysis,*further*supporting*the*contention*that*differing*mental*practices*have*

dissociable*and*identifiable*neural*correlates.*

* A*case*study*involving*a*single*highly_experienced*practitioner*engaging*in*a*

pratyahara*(sense_withdrawal)*practice*is*similarly*informative*(Kakigi*et*al.,*2005).*

Compared*to*painful*stimulation*when*not*engaging*in*meditation,*which*led*to*

recruitment*of*all*the*regions*commonly*implicated*in*pain*processing,*during*meditation*

there*was*a*marked*deactivation*of*these*classic*pain*areas,*including*the*thalamus,*

secondary*somatosensory*cortex,*insula,*and*cingulate*cortex.*Again,*none*of*the*four*



practice*types*meta_analyzed*here*bears*much*resemblance*to*this*pattern*(and*open*

monitoring*seems*almost*antithetical*to*it*–*in*line*with*the*methods*and*motivations*

underlying*each*practice).**

* Finally,*a*single*study*investigating*non8dual!awareness*in*highly*experienced*

Tibetan*Buddhist*practitioners*reported*evidence*that*this*practice*decreased*the*anti_

correlation*between*activity*in*‘extrinsic’*and*‘intrinsic’*networks*of*the*brain,*which*are*

argued*to*mediate*attention*to*the*external*environment*and*internal*states,*respectively*

(Josipovic*et*al.,*2011).*The*authors*created*numerous*regions_of_interest*throughout*the*

brain*corresponding*to*an*‘extrinsic’*network*for*attention*to*external*stimuli,*and*an*

‘intrinsic’*network*thought*to*be*involved*in*internal*streams*of*thought*(which*roughly*

parallels*the*default*mode*network).*The*extrinsic*and*intrinsic*networks*are*thought*to*

show*anti_correlated*patterns*of*functional*connectivity*during*either*external*tasks*or*

attention*to*internal*streams*of*thought*(e.g.,*during*mind_wandering)*(Fox*et*al.,*2005).*

The*authors*examined*the*extent*to*which*this*anti_correlated*functional*connectivity*

might*be*attenuated*by*non_dual*awareness*meditation,*which*broadly*aims*at*reducing*

the*sense*of*a*division*between*external*and*internal.*During*non_dual*awareness*

meditation,*the*anti_correlation*between*these*two*networks*was*markedly*attenuated*

compared*to*either*focused*attention*meditation*or*passive*fixation.*The*authors*

interpreted*these*results*as*evidence*of*the*effectiveness*of*non_dual*awareness*practice*at*

dissolving*the*boundary*between*internal*and*external*experiences*(i.e.,*subject_object*

duality;*Josipovic*et*al.,*2011).*In*line*with*our*central*hypothesis*and*meta_analytic*results,*

the*authors*also*suggested*that*their*results*indicated*that*non_dual*awareness*practice*is*



differentiable*at*the*neural*level*from*other*meditations,*such*as*focused*attention*and*

open*monitoring*meditation*(Josipovic*et*al.,*2011).*

* *Although*the*evidence*regarding*these*other*forms*of*meditation*remains*tentative,*

it*seems*clear*that*further*research*is*warranted*into*various*other*techniques*that*have*

not*yet*been*intensively*investigated.*Based*on*our*meta_analytic*findings,*as*well*as*the*

studies*just*reviewed,*we*suspect*that*future*work*will*discover*and*refine*dissociable*

neural*correlates*associated*with*these*various*psychologically*unique*meditation*

practices.*

!

5.8!Are!contemplative!practices!dissociable!by!electrophysiological!and!neurochemical!

measures?!

Virtually*all*of*the*meta_analytic*results*and*discussion*in*this*review*have*relied*on*

brain*signals*indicative*of*cerebral*blood*flow*(PET)*or*blood*oxygenation*(fMRI),*but*there*

are*numerous*other*ways*of*characterizing*brain*function,*most*notably*via*

electrophysiological*activity*(via*electroencephalography,*for*instance;*EEG)*and*at*the*

neurochemical*level*(i.e.,*the*tonal*and*phasic*rates*of*release*of*various*neurotransmitters*

across*different*areas*of*the*brain).*For*more*details*on*how*these*possibilities*have*been*

applied*in*meditation*research,*see*the*Supplementary*Discussion.*

!

5.9!Do!functional!neural!effects!associated!with!meditation!have!practical!significance?!

! Our*effect*size*meta_analyses*found*that*the*four*primary*categories*of*meditation*

examined*were*all*associated*with*approximately*‘medium’*effect*sizes*(mean*Cohen’s*d*=*

0.60*for*activations*and*_0.74*for*deactivations;*for*details*see*Tables*7*and*8).*Although*we*



find*these*results*both*reasonable*(in*magnitude)*and*encouraging,*we*reiterate*that*the*

‘meaningfulness’*of*effect*sizes*is*ultimately*arbitrary*even*where*their*use*is*highly*

developed*(e.g.,*in*the*behavioral,*social,*and*medical*sciences;*Cohen,*1992).*This*is*all*the*

more*true*in*neuroimaging,*where*their*calculation*and*interpretation*are*poorly*

understood*(see*Supplementary*Methods).*Nonetheless,*some*general*observations*can*be*

made.*

* First,*positive*and*negative*effect*sizes*(representing*activations*and*deactivations*

associated*with*meditation,*respectively)*are*similar*in*magnitude*(Tables*7*and*8;*Fig.*9).*

This*is*in*line*with*our*meta_analytic*neuroimaging*findings*(where*brain*deactivations*

were*nearly*as*common*and*significant*as*activations)*and*supports*the*idea*that*the*

successful*execution*of*a*particular*meditation*may*depend*as*much*on*which*brain*areas*

are*disengaged*as*on*which*are*actively*recruited.*

! Second,*the*approximately*‘medium’*magnitude*of*the*effects*suggests*that*the*

functional*neural*effects*of*meditation*result*in*roughly*a*one_half*standard*deviation*

increase*or*decrease*in*brain*activity,*relative*to*various*other*baseline*conditions,*or*

novices*attempting*to*execute*the*same*practice*as*experts.**

* Third,*differing*meditation*categories*showed*largely*similar*mean*effect*sizes*–*

roughly*one*half*to*two_thirds*of*a*standard*deviation*(Cohen’s*d*~0.50*–*0.67;*see*Table*8).*

The*exception*was*mantra*recitation,*which*appeared*to*result*in*larger*effects*for*both*

activations*and*deactivations*(Cohen’s*d!>*1.0).*This*apparently*large*difference*is*highly*

questionable,*however:*first,*these*‘mean’*(+)*and*(–)*effect*sizes*across*studies*are*in*fact*

simply*mean*effect*sizes*for*a*single*study*each,*as*only*two*studies*contributed*to*the*

effect*size*meta_analysis*for*mantra*recitation*(see*Tables*7*and*8).*Moreover,*the*two*



studies*that*contributed*(Davanger*et*al.,*2010,*Kalyani*et*al.,*2011)*have*among*the*

smallest*sample*sizes*of*any*studies*we*investigated*here*(see*Table*7).*This*makes*these*

reports*highly*susceptible*to*the*inflationary*biasing*of*effect*sizes*we*discussed*at*length*

in*the*Supplementary*Methods.*We*therefore*conclude*that*it*would*be*highly*premature*to*

argue*that*mantra*meditation*results*in*larger*effects*than*other*forms*of*meditation*

practice.*A*more*plausible*interpretation*is*that*inflationary*bias*was*larger*in*these*

studies,*and*the*true*effect*size*of*mantra*recitation*is*in*fact*comparable*to*the*other*

practices*examined*here.*

* Fourth,*a*funnel*plot*(scatterplot*of*effect*size*vs.*sample*size;*Fig.*6)*showed*a*

conspicuous*dearth*of*null*results*or*small*effect*sizes*(even*after*our*multiple*deflationary*

adjustments*of*originally*reported*effect*sizes),*for*both*‘positive’*effect*sizes*(brain*

activations)*and*‘negative’*effect*sizes*(brain*deactivations).*The*simplest*interpretation*of*

these*results*is*that*fairly*serious*publication*bias*(i.e.*non_publication*of*null*and*‘non_

significant’*findings)*afflicts*this*field.*Even*if*meditation*always*and*truly*results*in*

significant*effects*on*brain*activation*or*deactivation,*given*that*78*functional*

neuroimaging*studies*had*been*published*at*the*time*of*writing,*we*would*expect*at*least*a*

few*null*results*to*have*been*obtained*and*reported*simply*by*chance*alone.*An*alternative*

(albeit*related)*explanation*is*that*smaller*effect*sizes*were*not*observed*precisely*because*

of*the*inflationary*bias*inherent*in*neuroimaging*reporting*of*effect*sizes*(see*section*2.5).*

Although*this*possibility*presents*at*least*as*large*a*problem*as*does*publication*bias,*it*

shifts*the*emphasis*from*the*limitations*of*the*current*scientific*publication*model*(which*

places*undue*emphasis*on*‘positive’*findings)*to*the*limitations*of*neuroimaging*data*

analysis*and*reporting*practices.*In*either*case,*the*lack*of*reported*small*or*null*effects*in*



this*literature*(even*after*our*severe*deflationary*procedures)*suggests*bias*at*some*stage*

of*study*design,*analysis,*or*reporting.**

That*said,*for*both*negative*and*positive*effect*sizes,*the*expected*funnel*plot*

pattern*was*generally*observed:*that*is,*with*increasing*sample*size,*the*variability*among*

effect*sizes*reported*decreased*drastically;*and*notably,*the*most*extreme*effect*sizes*were*

always*reported*in*studies*with*the*smallest*sample*sizes.*This*suggests,*encouragingly,*

that*despite*potential*publication*bias*or*inflationary*bias*due*to*neuroimaging*analysis*

methods,*nonetheless*studies*with*larger*samples*tend*to*converge*on*similar*and*more*

reasonable*(medium)*effect*sizes.*Although*such*a*conclusion*is*tentative,*the*results*to*

date*(Fig.*6)*suggest*that*a*sample*size*of*approximately*n!=*25*is*sufficient*to*reliably*

produce*effect*sizes*that*accord*with*those*reported*in*studies*with*much*larger*samples*

(up*to*n!*=*46).*

!

5.10!Meditation,!the!brain,!and!clinical!disorders!

* Although*the*central*aim*of*this*meta_analysis*was*to*better*delineate*the*neural*

correlates*of*meditation*in*healthy*practitioners,*the*potential*effects*of*meditation*on*

various*physical*and*psychological*clinical*conditions*is*of*enormous*interest*(Gotink*et*al.,*

2015)*and*therefore*warrants*a*brief*discussion.*To*our*knowledge,*only*five+studies*to*

date*(Table*S1)*have*examined*the*relationship*between*meditation,*brain*activity,*and*

clinical*disorders*of*some*kind.*One*study*investigated*social*anxiety*disorder*(Goldin*and*

Gross,*2010)*and*another*bipolar*disorder*(Ives_Deliperi*et*al.,*2013);*one*examined*

patients*with*breast*cancer*(Monti*et*al.,*2012);*one*involved*chronic*tobacco*smokers*

during*a*period*of*abstinence*from*smoking*(Westbrook*et*al.,*2013);*and*one*recruited*



patients*with*mild*cognitive*impairment*(Wells*et*al.,*2013).*The*heterogeneity*of*these*

investigations*precludes*any*quantitative*meta_analytic*procedure,*but*nonetheless*these*

preliminary*explorations*are*a*very*important*step*toward*examining*the*potential*of*

meditation*to*ameliorate*such*conditions,*as*well*as*understanding*the*cognitive*and*

neural*mechanisms*by*which*these*improvements*might*take*place.*Considering*the*fairly*

ample*evidence*from*psychological*research*that*meditation*can*have*salutary*effects*on*

affective*characteristics*(Sedlmeier*et*al.,*2012,*Goyal*et*al.,*2014),*further*investigations*

into*its*potential*benefits*for*clinical*conditions,*and*the*brain*mechanisms*related*to*these*

benefits,*are*of*paramount*importance.**

*

5.11!Meta8analytic!limitations!

First,*it*should*be*reiterated*that*the*four*categories*employed*in*our*synthesis**

combined*meditation*practices*which,*although*similar,*are*not*necessarily*identical.*

Moreover,*there*are*several*other*major*categories*of*meditation*that*could*not*be*

quantitatively*examined*here*(e.g.,*non_dual*awareness*and*sensory_withdrawal*practices),*

due*to*the*paucity*of*empirical*data*to*date*(see*Section*1.3).*

Second,*despite*inclusion*of*all*eligible*studies*to*date,*the*present*analysis*relies*on*

relatively*few*research*reports*(n*=*25;*see*Table*1).*We*also*combined*results*from*long_

term*practitioners*with*those*of*novices*undergoing*short_term*training*in*an*effort*to*

include*all*available*data*(see*Table*2).*This*may*be*problematic*because,*as*noted*earlier,*

the*diverse*goals*of*meditation*practices*can*take*considerable*time*to*be*realized.*It*might*

therefore*be*expected*that*the*distinctions*between*brain*activation*patterns*driven*by*

particular*forms*of*meditation*may*be*even*sharper*among*expert*vs.*novice*practitioners,*



or*that*brain*activity*in*novices*might*otherwise*influence*or*drive*the*effects*observed*

here.*To*mitigate*these*concerns,*however,*we*conducted*a*series*of*four*supplemental*

meta_analyses*where*we*excluded*studies*of*short_term*meditation*training,*and*found*

little*evidence*that*this*was*the*case.*Meta_analytic*results*for*each*meditation*category*

employing*only*long_term*practitioners*were*negligibly*different*from*our*main*meta_

analyses,*except*in*the*case*of*open*monitoring*meditation.*In*the*case*of*open*monitoring*

meditation,*the*general*pattern*of*results*was*also*similar,*but*the*precise*locations*and*

significance*levels*of*various*clusters*were*different*(for*details,*compare*Table*5*with*

Table*S4).+

Third,*study*methods*and*practitioner*samples*were*highly*heterogeneous.*Both*

meditation*and*baseline*conditions*differed*considerably*across*studies*(even*within*a*

single*meditation*category),*as*did*meditation*experience*level*(even*among*expert*

practitioners).*

Fourth,*numerous*and*serious*difficulties*attend*the*calculation*and*interpretation*

of*effect*sizes*in*neuroimaging*data.*Our*results*in*this*sphere,*and*their*bearing*on*the*

question*of*the*‘practical*significance’*of*meditation’s*effects*on*brain*function,*need*to*be*

viewed*in*light*of*the*many*caveats*and*limitations*we*have*discussed*at*length*in*the*

Supplementary*Methods.*

Future*work*may*be*better*able*to*mitigate*many*of*these*limitations*by*directly*

examining*multiple*forms*of*meditation*within*the*same*practitioners*and/or*within!the*

same*study,*and*using*more*homogenous*baseline/control*conditions*(e.g.,*Brewer*et*al.,*

2011).*Such*an*approach*would*control*for*many*of*the*potential*confounds*that*plague*

comparison*across*different*studies,*conducted*by*different*researchers,*investigating*



different*samples*of*practitioners.*Taken*together,*the*present*results*should*be*

interpreted*with*caution:*a*clearer*understanding*of*the*major*categories*of*meditation,*as*

well*as*their*subtler*subdivisions,*awaits*further*research*undertaken*with*more*directly*

comparable*methods,*baselines,*and*populations.*

!

5.12!Other!methodological!challenges!in!the!neuroimaging!of!meditation!

* Other*major*concerns*have*less*to*do*with*meta_analytics*or*statistical*issues,*but*

rather*relate*specifically*to*the*investigation*of*meditation*practitioners.*Several*important*

themes*are*outlined*here.*

* 5.12.1+Lifestyle+variables.+The*first*concern*is*the*general*and*unknown*effect*of*

lifestyle.*Highly_experienced*meditation*practitioners*are*likely*to*have*more*meager*

(calorie_restricted)*and*more*vegetarian*diets;*are*less*likely*to*have*children*or*long_term*

regular*employment;*and*probably*sleep*less*than*the*average*person*(Britton*et*al.,*2014).*

These*are*just*a*few*major*examples;*an*array*of*other*factors*might*be*relevant.*Different*

meditation*traditions*emphasize*such*factors*to*varying*degrees,*and*it*is*certainly*

conceivable*that*major*differences*in*diet,*stress,*and*sleeping*patterns*could*have*effects*

on*brain*structure*and*function.*Control*subjects*in*the*studies*meta_analyzed*here,*

however,*typically*only*control*for*simple*variables*like*age,*sex,*and*sometimes*

handedness,*and*are*therefore*unable*to*account*for*these*lifestyle*variables.*Until*these*

and*other*factors*are*carefully*controlled*for,*the*potentially*confounding*effects*of*non_

meditation_specific*aspects*of*the*contemplative*lifestyle*cannot*be*ruled*out*or*fully*

understood*(Fox*et*al.,*2014).*



* 5.12.2+Pre?existing+differences+in+brain+structure+and+function.*A*second*

general*concern*is*the*possibility*of*pre8existing!differences*in*brain*structure*or*function*in*

advanced*meditation*practitioners*(Fox*et*al.,*2014).*Given*the*rigorous*and*peculiar*

demands*of*spending*thousands*of*hours*in*solitary,*minimally_stimulating*environments*

and*unusual*(for*Western*practitioners)*and*often*painful*physical*postures,*it*seems*

highly*likely*that*long_term*contemplative*practice*may*preferentially*attract*persons*with*

a*proclivity*toward*solitude*and*sustained*attention*to*inner*mental*life.*Support*for*this*

hypothesis*comes*from*a*recent*study*that*was*able*to*predict*subsequent*practice*of*two*

different*forms*of*meditation*(mindfulness*and*compassion)*from*baseline*brain*activity*

alone*(Mascaro*et*al.,*2013).*Cross_sectional*studies*(which*form*a*large*part*of*this*meta_

analytic*dataset)*cannot*control*for*such*pre_existing*differences.*On*the*other*hand,*

studies*involving*short_term*training*of*novices*in*pre_post*designs*cannot*examine*the*

potentially*subtle*effects*that*long_term*and*committed*practice*may*have*on*brain*

function.*Future*work*will*have*to*strike*a*balance*somewhere*between*the*limitations*of*

these*two*general*approaches,*and*further*studies*of*pre_existing*(and*potentially*

predictive)*differences*in*brain*structure*and*function*in*meditation*practitioners*would*be*

highly*beneficial*(cf.*Mascaro*et*al.,*2013).**

5.12.3+‘Overshadowing.’*A*third*and*major*concern*is*what*we*call*

‘overshadowing’*–*the*possibility*that*a*practitioner’s*background*experience*with*a*variety*

of*meditation*techniques*might*color*the*neurophysiological*results*obtained*during*the*

brief*‘state’*investigations*of*isolated*meditation*techniques*that*are*typical*of*the*

experiments*examined*here.*This*issue*is*discussed*further*in*the*Supplementary*

Discussion.*



5.12.4+Enduring+trait+differences+in+brain+and+cognitive+function.*Closely*

related*to*the*overshadowing*effect*are*unknown*trait*differences.*By*‘overshadowing’*we*

mean*the*possibility*that*accumulated*trait*differences*might*overshadow*(or*interact*

with)*brain*activations*and*deactivations*directly*associated*with*a*brief,*induced*state!of*

meditation*in*neuroimaging*investigations.*But*although*these*putative*trait*differences*are*

a*potential*confounding*factor*for*our*purposes*here*(investigating*meditation*state*

effects),*enduring*trait*changes*are*an*explicit*goal*of*most*meditation*traditions,*and*are*a*

worthy*object*of*study*in*their*own*right.*Here,*we*chose*to*exclude*such*studies*from*our*

meta_analysis*(criterion*iv;*see*Methods*section*2.1.2),*mainly*because*of*the*enormous*

methodological*challenges*involved*in*synthesizing*across*so*many*disparate*tasks*and*

contemplative*traditions.*Although*our*meta_analysis*was*also*affected*by*differing*

baseline/comparison*conditions,*and*potentially*also*an*‘overshadowing’*effect,*

nonetheless*the*meditation*states*investigated*were*constant*and*consistent*for*each*

analysis*(focused*attention,*mantra*meditation,*etc.).*The*major*challenge*facing*any*effort*

to*synthesize*trait*effects*associated*with*meditation*practice*is*that*even*this*limited*

homogeneity*(constant*meditation*states,*despite*differing*samples*and*comparison*

conditions)*is*absent.*Not*only*is*there*great*heterogeneity*among*the*tasks*on*which*

meditation_related*traits*are*being*investigated*(e.g.,*emotion*regulation,*perceptual*

discrimination,*etc.),*no*consistent*meditation*state*is*being*induced,*and*the*practitioners*

employed*will*invariably*possess*heterogeneous*contemplative*backgrounds*with*respect*

to*the*proportion,*and*absolute*amount,*of*time*spent*in*various*different*practices.*One*

way*to*begin*to*examine*such*trait*differences,*which*sidesteps*these*problems,*would*be*



to*compile*data*on*long_term*practitioners*during*the*‘resting’*state,*for*instance*measuring*

changes*in*functional*connectivity*at*baseline*(in*the*absence*of*any*task*or*stimuli).*

+ 5.12.5+Integration+of+functional+neuroimaging+methods+with+behavioral+

measures.+As*we*discussed*in*our*previous*meta_analysis*of*morphometric*neuroimaging*

studies*of*meditation*(Fox*et*al.,*2014),*alterations*in*brain*structure*and*function*are*of*

little*value*(beyond*basic*scientific*interest)*if*they*are*not*accompanied*by*changes*in*

behavior*or*cognitive_emotional*experience*and*wellbeing*(Fox*et*al.,*in*press).*We*discuss*

this*issue*and*some*of*the*findings*we*reviewed*related*to*brain_behavior*correlations*in*

the*Supplementary*Discussion.*

!

5.13!Summary!and!conclusions!

The*present*meta_analysis*is*the*first*to*report*dissociable*patterns*of*brain*

activation*and*deactivation*underlying*four*major*categories*of*meditation*(focused*

attention,*mantra*recitation,*open*monitoring,*and*loving_kindness/compassion*practices),*

and*provides*suggestive*evidence*for*the*dissociability*of*three*additional*meditation*types*

(visualization,*sense_withdrawal,*and*non_dual*awareness*practices).*Our*synthesis*

provides*preliminary*evidence*for*largely*dissociable*neural*substrates*which,*broadly*

speaking,*are*consistent*with*the*methods,*aims,*and*putative*psychological*results*of*the*

practices*examined.*Collectively,*these*results*suggest*that*while*several*regions*may*be*

equally*involved*in*many*forms*of*contemplative*practice*(Sperduti*et*al.,*2012),*

differences*in*neural*activity*greatly*outnumber*similarities.*Commonality!across!

meditation!categories!is!the!exception!rather!than!the!rule.*Importantly,*deactivations*

almost*always*accompany*activations*(though*they*are*usually*fewer*in*number,*less*



substantial*in*terms*of*cluster*size,*and*less*consistent*across*studies*in*terms*of*peak*

likelihood*value).*This*suggests*that*for*the*effective*execution*of*various*meditation*

practices,*disengaging*particular*brain*regions*may*be*nearly*as*important*as*engaging*

others.**

After*careful*corrections*and*adjustments*for*suspected*inflationary*biases,*effect*

size*meta_analysis*suggests*that*meditation*practices*tend*to*yield*approximately*medium_

sized*effects.*These*results*suggest*that*meditation’s*relationship*with*brain*function*may*

be*practically*significant,*but*there*appears*to*be*a*long*way*to*go*in*the*statistical*theory*of*

neuroimaging*before*these*findings*can*be*interpreted*with*confidence.*Moreover,*it*is*

imperative*that*neuroimaging*investigations*of*meditation*begin*to*rigorously*relate*

findings*to*behavioral*and*self_reported*outcomes,*in*order*to*understand*how*(and*to*

what*extent)*these*changes*in*brain*activity*are*related*to*actual*cognitive_affective*change*

and*benefits*in*practitioners.*

Many*have*understandably*viewed*the*nascent*neuroscience*of*meditation*with*

skepticism*(Andresen,*2000,*Horgan,*2004),*but*recent*years*have*seen*an*increasing*

number*of*high_quality,*controlled*studies*that*are*suitable*for*inclusion*in*meta_analyses*

and*that*can*advance*our*cumulative*knowledge*of*the*neural*basis*of*various*meditation*

practices*(Tang*et*al.,*2015).*With*nearly*a*hundred*functional*neuroimaging*studies*of*

meditation*now*reported,*we*can*conclude*with*some*confidence*that*different*practices*

show*relatively*distinct*patterns*of*brain*activity,*and*that*the*magnitude*of*associated*

effects*on*brain*function*may*have*some*practical*significance.*The*only*totally*

incontrovertible*conclusion,*however,*is*that*much*work*remains*to*be*done*to*confirm*and*

build*upon*these*initial*findings.*



Acknowledgments*

We*thank*Dr.*Antoine*Lutz*and*Dr.*David*M.*Fresco*for*very*helpful*discussions*of*

the*methods*and*results*of*this*meta_analysis.*We*also*thank*Dr.*Norman*Farb*for*

providing*further*details*from*previously*unpublished*data*that*contributed*to*the*effect*

size*meta_analysis.*This*work*was*supported*in*part*by*Natural*Sciences*and*Engineering*

Research*Council*(NSERC)*Vanier*Canada*Graduate*Scholarships*awarded*to*K.C.R.F.*and*

M.L.;*NSERC*Canada*Graduate*Scholarships*awarded*to*M.L.D.*and*M.E.;*a*University*of*

British*Columbia*Affiliated*Doctoral*Fellowship*awarded*to*J.L.F.;*and*NSERC*and*Canadian*

Institute*of*Health*Research*(CIHR)*grants*awarded*to*K.C.+

+

+ +



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**

* *



+

•+SUPPLEMENTARY+MATERIAL+•+

+

Functional+neuroanatomy+of+meditation:+A+review+and+meta?analysis+of+78+functional+

neuroimaging+investigations+

Kieran*C.*R.*Foxa,*,*Matthew*L.*Dixona,*Savannah*Nijeboera,*Manesh*Girna,*James*L.*Flomanb,*

Michael*Lifshitzc,*Melissa*Ellamild,*Peter*Sedlmeiere,*and*Kalina*Christoffa,e*

*

a*Department*of*Psychology,*University*of*British*Columbia,*2136*West*Mall,*Vancouver,*

B.C.,*V6T*1Z4*Canada*

b*Department*of*Educational*and*Counselling*Psychology,*and*Special*Education,*University*

of*British*Columbia,*2125*Main*Mall,*Vancouver,*B.C.,*V6T*1Z4*

c*Integrated*Program*in*Neuroscience,*McGill*University,*3775*University*St.,*Montreal,*QC,*

H3A*2B4*

d*Neuroanatomy*and*Connectivity*Research*Group,*Max*Planck*Institute*for*Human*

Cognitive*and*Brain*Sciences,*Stephanstrasse*1a,*Leipzig,*Germany*04103.*

e*Institut*für*Psychologie,*Technische*Universität*Chemnitz,*43*Wilhelm_Raabe*Street,*

Chemnitz,*Germany*

e*Brain*Research*Centre,*University*of*British*Columbia,*2211*Wesbrook*Mall,*Vancouver,*

B.C.,*V6T*2B5*Canada*

**To*whom*correspondence*may*be*addressed*(at*address*a*above).*Telephone:*1_778_968_

3334;*Fax:*1_604_822_6923;*E_mail:*[email protected]*

*



Supplementary+Methods++!

Further!details!regarding!excluded!studies!

About*two_thirds*(52*of*78)*of*all*studies*did*not*meet*with*one*or*more*of*our*

inclusion*criteria*(Table*S1).*This*fact*should*not*be*considered*an*indication*of*the*poor*

quality*of*these*studies;*only*a*small*minority*was*excluded*because*of*methodological*

problems*(details*in*Table*S1).*Many*studies*were*excluded*simply*because*their*design*or*

analyses*were*not*amenable*to*our*meta_analytic*methods*and*questions,*with*criteria*(i)*

and*(iv)*accounting*for*the*vast*majority*of*exclusions*(Table*S1).*For*instance,*many*

studies*were*excluded*because*they*did*not*have*participants*actually*engage*in*meditation*

practice*in*the*scanner:*these*studies*were*interested*instead*in*the*effect*of*prior*

meditation*training*on*the*neural*correlates*of*various*other*tasks*during*scanning,*

whereas*our!interest!was!in!neural!correlates!of!the!meditation!practices!themselves.**

Mantra*recitation*bears*some*resemblance*to*prayer,*but*differs*in*several*

important*ways.*For*example,*mantra*recitation*is*typically*impersonal*(the*practitioner*

may*not*even*know*the*meaning*of*the*words*being*recited,*which*are*often*in*an*ancient*

and*unfamiliar*language,*such*as*Sanskrit),*whereas*prayer*often*involves*a*personal*

request*with*meaningful*content.*Mantra*recitation*is*also*often*recited*in*a*manner*that*

deliberately*matches*the*recitation*to*the*rhythm*of*inhalation*and*exhalation,*thus*

drawing*attention*toward*interoceptive*information,*whereas*prayer*does*not*typically*

have*this*component.*Therefore,*the*handful*of*studies*that*have*investigated*various*

forms*of*Judeo_Christian*prayer*(e.g.,*(Schjoedt*et*al.,*2009,*Schjoedt*et*al.,*2010)*were*not*

included*in*our*analyses*here.*



Several*other*studies*pursued*the*question*of*meditation*training’s*relationship*to*

various*clinical*conditions*and*the*brain.*Despite*the*high*value*of*such*studies,*their*

inclusion*would*present*a*serious*confound*to*our*meta_analytic*results*and*so*these*

studies*too*were*excluded.*On*the*other*hand,*many*studies*(16*of*78)*were*excluded*

because*they*did*not*report*full*tables*of*voxel*coordinates*of*peak*difference*for*the*

contrast*of*interest*(meditation*>*some*other*condition).*Although*some*of*these*studies*

might*have*been*excluded*in*any*case*(for*a*variety*of*other*reasons),*nonetheless*the*

failure*to*report*full*voxel*coordinates*represents*a*serious*and*unfortunate*loss*of*data*for*

meta_analyses.*

*

Instructions!given!in!loving8kindness!and!compassion!meditation!studies!

* * Likely*the*category*in*our*meta_analysis*with*the*greatest*potential*for*variation*

among*studies*is*the*loving_kindness/compassion*group.*Upon*reviewing*the*instructions*

given*to*participants*in*these*six*studies,*however,*we*found*that*overall*the*similarities*

greatly*outweighed*the*differences:*broadly*speaking,*all*studies*had*participants*generate*

positive*emotions*(loving_kindness,*well_wishing,*compassion,*etc.)*toward*others*and/or*

in*a*general,*non_referential*way.*Here*we*reproduce*the*exact*instructions*given*in*each*

study*for*the*reader’s*convenience.*

*

•*Lou*et*al.*(1999):*“…experience*of*joy*and*happiness*in*abstract*form*(i.e.,**not*related*to*

external*events*or*facts).”*

•*Lutz*et*al.*(2008):*“During*the*training*session,*the*subject*will*think*about*someone*he*



cares*about,*such*as*his*parents,*sibling*or*beloved,*and*will*let*his*mind*be*invaded*by*a*

feeling*of*altruistic*love*(wishing*well_being)*or*of*compassion*(wishing*freedom*from*

suffering)*toward*these*persons.*After*some*training*the*subject*will*generate*such*feeling*

toward*all*beings*and*without*thinking*specifically*about*someone.*While*in*the*scanner,*

the*subject*will*try*to*generate*this*state*of*loving*kindness*and*compassion.”*

•*Lutz*et*al.*(2009):*Same*as*Lutz*et*al.*(2008).*

•*Brewer*et*al.*(2011):*“Please*think*of*a*time*when*you*genuinely*wished*someone*well*

(pause).*Using*this*feeling*as*a*focus,*silently*wish*all*beings*well,*by*repeating*a*few*short*

phrases*of*your*choosing*over*and*over.*For*example:*May*all*beings*be*happy,*may*all*

beings*be*healthy,*may*all*beings*be*safe*from*harm.”*

•*Lee*et*al.*(2012):*Specific*instructions*not*provided,*but*described*as*“very*similar”*(p.*3)*

to*those*used*in*Lutz*et*al.*(2008)*and*(2009).**

•*Weng*et*al.*(2014):*“Participants*practiced*compassion*for*targets*by*1)*contemplating*

and*envisioning*their*suffering*and*then*2)*wishing*them*freedom*from*that*suffering.*They*

first*practiced*compassion*for*a*Loved*One,*such*as*a*friend*or*family*member.*They*

imagined*a*time*their*loved*one*had*suffered*(e.g.,*illness,*injury,*relationship*problem),*

and*were*instructed*to*pay*attention*to*the*emotions*and*sensations*this*evoked.*They*

practiced*wishing*that*the*suffering*were*relieved*and*repeated*the*phrases,*“May*you*be*

free*from*this*suffering.*May*you*have*joy*and*happiness.”*They*also*envisioned*a*golden*

light*that*extended*from*their*heart*to*the*loved*one,*which*helped*to*ease*his/her*

suffering.*They*were*also*instructed*to*pay*attention*to*bodily*sensations,*particularly*



around*the*heart.*They*repeated*this*procedure*for*the*Self,*a*Stranger,*and*a*Difficult*

Person.*The*Stranger*was*someone*encountered*in*daily*life*but*not*well*known*(e.g.,*a*bus*

driver*or*someone*on*the*street),*and*the*Difficult*Person*was*someone*with*whom*there*

was*conflict*(e.g.,*coworker,*significant*other).*Participants*envisioned*hypothetical*

situations*of*suffering*for*the*stranger*and*difficult*person*(if*needed)*such*as*having*an*

illness*or*experiencing*a*failure.*At*the*end*of*the*meditation,*compassion*was*extended*

towards*all*beings.*For*each*new*meditation*session,*participants*could*choose*to*use*

either*the*same*or*different*people*for*each*target*category*(e.g.,*for*the*loved*one*category,*

use*sister*one*day*and*use*father*the*next*day).”*

++Supplementary!neuroimaging!meta8analyses!

In*order*to*address*the*potential*confound*of*collapsing*across*studies*investigating*

long_term*practitioners,*and*those*involving*novices*undergoing*short_term*training,*we*

executed*a*series*of*supplementary*meta_analyses*where*all*studies*involving*short_term*

meditation*training*were*excluded.*This*allowed*us*to*ensure*that*the*potentially*large*

differences*observed*in*novices*learning*meditation*for*the*first*time*were*not*driving*our*

meta_analytic*results.**

Five*of*the*26*included*studies*involved*analyses*of*practitioners*engaging*in*short_

term*meditation*training*only*(Farb*et*al.,*2007,*Dickenson*et*al.,*2013,*Farb*et*al.,*2013b,*

Weng*et*al.,*2013,*Lutz*et*al.,*2014)*and*were*excluded*from*the*supplementary*meta_

analyses*(for*details,*see*Table*2).*Another*study*mixed*long_term*practitioners*and*

novices*in*its*sample*(Kalyani*et*al.,*2011)*and*did*not*report*results*separately*for*long_

term*practitioners,*and*was*therefore*also*excluded.*Another*study*also*employed*both*



long_term*and*short_term*practitioners*(Taylor*et*al.,*2011),*but*here*the*novice*

practitioners*served*as*the*comparison*group,*and*therefore*the*results*reported*from*this*

study*remained*valid*for*inclusion*in*the*supplementary*meta_analyses*(the*study*used*a*

between_group*design,*comparing*brain*activity*in*highly_experienced*practitioners*to*a*

less*experienced*group*–*consistent*with*the*other*reports*included*in*the*meta_analyses).*

Ultimately,*six*studies*were*excluded:*one*each*from*the*focused*attention*

(Dickenson*et*al.,*2013),*mantra*meditation*(Kalyani*et*al.,*2011),*and*loving_

kindness/compassion*(Weng*et*al.,*2013)*analyses,*and*three*studies*from*the*open*

monitoring*meta_analysis*(Farb*et*al.,*2007,*Farb*et*al.,*2013b,*Lutz*et*al.,*2014).*To*

anticipate*our*findings,*these*exclusions*generally*had*only*negligible*impact*on*our*meta_

analytic*results,*and*are*therefore*reported*below*in*the*Supplementary*Materials*Results.*

*

+Effect!size!meta8analysis:!Discussion!of!challenges,!methods,!and!equations!used!+

Should*effect*sizes*even*be*calculated*from*neuroimaging*data?*Intensive*debate*is*

ongoing*and*has*not*yet*provided*any*definitive*answers*(Kriegeskorte*et*al.,*2009,*Vul*et*

al.,*2009,*Friston,*2012).*There*appear*to*be*at*least*two*major*recurring*concerns.*The*first*

is*that,*typically,*only*maximum*t_statistics*are*reported*in*neuroimaging*analyses.*These*

statistics*represent*the*most*extreme*peak*for*the*voxel*showing*the*greatest*difference*

among*an*entire*cluster*of*significantly*different*voxels*–*the*rest*of*which*all*have*smaller*

(yet*still*significant)*t_statistics.*Therefore,*the*maximum*(or*‘peak’)*t_statistic*is*

necessarily*an*overestimate*of*the*average*cluster8wide*t_statistic,*which*is*rarely*reported.*

A*straightforward*(albeit*approximate*and*preliminary)*solution*to*this*problem,*which*we*

have*employed*before*(Fox*et*al.,*2014),*is*presented*below*(see*Section*2.5.6).*In*general,*



the*approach*is*to*adjust*(i.e.,*deflate)*the*calculated*effect*sizes*based*on*maximum/peak*

statistics,*so*that*they*are*more*conservative*and*more*representative*of*the*expected*

cluster8wide*values.*

A*second*major*concern*is*that*meta_analyses*of*mean*effect*sizes*should*also*

include*all*null*(non_significant)*results.*Null*results*are*rarely*reported*in*neuroimaging*

studies,*however.*Including*all*results*is*important*because*statistically*‘significant’*results*

need*not*be*large*in*magnitude,*particularly*if*sample*size*is*large:*with*a*large*enough*

sample,*even*very*small*differences*between*groups*that*are*trivial*for*practical*purposes*

can*yield*small*p_values*that*exceed*arbitrary_but_conventional*significance*thresholds*

(e.g.,*p*<.05).*Effect*size*meta_analysis*aims*to*comprehensively*include*even*non_

significant*results*for*the*simple*reason*that*an*effect*can*be*large*and*practically*

meaningful,*but*still*fail*to*attain*an*arbitrary*statistical*significance*threshold*due*to*small*

sample*size,*large*variability*in*the*data,*or*a*host*of*other*reasons*(Schmidt,*1992,*Schmidt*

and*Hunter,*1997).*By*impartially*including*all*reported*results*(regardless*of*statistical*

‘significance’)*effect*size*meta_analysis*aims*to*estimate*the*magnitude*of*true*effects*

relatively*independently*of*sample*size*or*arbitrarily*chosen*‘significance’*valuations*

(Schmidt,*1992,*Schmidt*and*Hunter,*1997).**

The*problem*is*that*standard*procedure*in*neuroimaging*studies*is*to*set*an*

arbitrary*significance*threshold*and*report*only*differences*that*exceed*this*value.*Such*a*

practice*produces*an*overwhelming*bias*toward*reporting*‘positive’*over*null*results,*a*

broader*problem*in*essentially*all*fields*of*research*(i.e.,*the*‘file*drawer’*problem;*

(Rosenthal,*1979).*Effect*sizes*based*solely*on*results*that*have*attained*statistical*

significance*(e.g.,*p*<*.05)*will*inevitably*overestimate*the*true*effect*size*(Schmidt,*1992).*



This*appears*to*be*all*the*more*true*for*‘underpowered’*studies*with*small*sample*sizes*

(Kraemer*et*al.,*1998).*

Noting*that*the*failure*to*publish*overall*null*findings*plagues*neuroimaging*

research*as*much*as*other*fields,*an*additional*problem*is*whether*to*report*within8study*

null*results.*Typical*neuroimaging*subtraction*contrasts*involve*thousands*(or*tens*of*

thousands)*of*independent*t_tests*across*the*many*voxels*in*the*brain.*Clearly,*reporting*all*

non_significant*results*would*be*impractical,*and*reporting*effect*sizes*for*only*a*small*

number*of*voxels*may*therefore*be*an*“unavoidable”*practice*in*neuroimaging*(Friston,*

2012).*For*this*same*reason,*peak*t_statistics*for*a*given*significant*cluster*are*usually*the*

only*values*reported:*unique*t_statistics*for*each*voxel*in*a*cluster*are*not*usually*reported*

because*this*could*still*amount*to*tens*or*hundreds*of*individual*results*to*be*listed.*

Therefore,*there*seems*to*be*fairly*reasonable*justification*for*the*practice*in*neuroimaging*

of*not*reporting*within8study*null*results*(and*even*significant,*non_peak*results*within*a*

cluster).**

Unfortunately,*this*approach*(a*practical*but*crude*solution*to*a*very*difficult*

problem)*introduces*an*unknown*amount*of*inflationary*bias*in*the*mean*effect*sizes*for*

neuroimaging*studies.*Monte*Carlo*simulations*suggest*that*this*inflationary*bias*becomes*

increasingly*large*at*more*stringent*significance*thresholds*(Lane*and*Dunlap,*1978,*Brand*

et*al.,*2008)*–*and*unfortunately,*highly*conservative*family_wise*error*corrections*are*the*

norm*in*neuroimaging*studies.*Although*various*cross_validation*methods*have*been*

suggested*to*correct*for*this*bias,*these*methods*necessarily*employ*some*of*the*data*for*

validation*and*only*the*remaining*portion*for*estimating*effects*themselves,*and*are*

therefore*bound*to*miss*an*unknown*number*of*effects*(Friston,*2012).*



Theoretical*arguments*have*been*made,*however,*that*this*problem*may*be*less*

severe*in*neuroimaging*than*(for*instance)*behavioral*or*clinical*investigations.*Due*to*the*

high*cost*of*neuroimaging,*studies*almost*always*involve*small*sample*sizes*(typically,*N*=*

10_20).*Indeed,*for*the*studies*included*in*the*present*meta_analysis,*samples*were*as*

small*as*just*4*subjects*in*one*repeated_measures*design*(Davanger*et*al.,*2010),*and*the*

mean*sample*size*(including*controls)*across*all*included*studies*was*only*~22*subjects*

(see*Table*2).*The*argument*is*that*smaller*sample*sizes*actually*have*the*benefit*of*

rendering*it*less*likely*that*sample*size*alone*will*drive*‘significant’*effects*(Friston*et*al.,*

1999,*Friston,*2012).*But*this*reasoning*only*goes*so*far:*stringent*significance*thresholds*

for*the*t_tests*upon*which*the*effect*sizes*are*based,*combined*with*low*statistical*power,*

will*nonetheless*produce*inflations*of*the*reported*effects*compared*to*the*true*effect*size,*

due*to*an*unintentional*publication*bias*toward*‘significant’*results*(Schmidt,*1992,*

Yarkoni,*2009,*Yarkoni*et*al.,*2010,*Hupé,*2015).*Additionally,*underpowered*studies*are*

more*likely*to*demonstrate*issues*with*replicability*and*reliability,*presenting*a*challenge*

to*developing*a*robust*evidence*base*in*any*field*of*research*(Cumming,*2012,*2013).*

Calculation+of+effect+sizes+(Cohen’s+d).+Wherever*possible,*we*used*studies’*t8

statistics*of*group*differences*between*brain*activations*of*meditators*vs.*controls,*or*of*

meditation*practitioners*before*and*after*short_term*training,*to*calculate*an*effect*size*

(Cohen’s*d)*for*each*result,*using*Equation*1*(Ray*and*Shadish,*1996):+

! = !! !!!+ !

!!*********(1)**



In*this*equation,*t*is*the*value*of*the*reported*peak*t_statistic,*and*ne!and*nc*are*the*sample*

sizes*for*experimental*(meditation)*and*control*groups,*respectively*(see*section*2.5.3*for*

justification*of*the*use*of*this*equation*with*repeated_measures*designs).*

Occasionally,*where*only!F_statistics*were*provided,*effect*sizes*were*calculated*

using*the*online*Practical*Meta_Analysis*Effect*Size*Calculator*(Lipsey*and*Wilson,*2001)*

maintained*by*the*Campbell*Collaboration*(available*at:*

http://www.campbellcollaboration.org/escalc/html/EffectSizeCalculator_Home.php).*

Studies*reporting*only*p8values*or*Z!scores*were*not*included*in*the*effect*size*meta_

analysis*because*of*the*inherent*difficulty*of*calculating*effect*sizes*from*these*statistics*

without*access*to*original*datasets.*

Calculating+effect+sizes+for+repeated?measures+designs.+Many*of*the*studies*

examined*here*involve*some*form*of*repeated_measures*design,*in*that*they*compared*

brain*activation*in*meditation*practitioners*with*these*practitioners’*own*brain*activity*

during*different*tasks*(e.g.,*resting*and*not*meditating)*or*at*various*time_points*(e.g.,*pre_*

and*post_training*in*a*meditation*technique).**

Although*fairly*simple*solutions*for*calculating*effect*sizes*from*t_statistics*derived*

from*repeated_measures*designs*have*been*proposed,*unfortunately*the*information*

required*to*do*so*(namely,*the*correlation*between*the*scores*being*compared*in*the*t_test)*

is*almost*never*reported*(Dunlap*et*al.,*1996).*Using*Monte*Carlo*simulations,*however,*

Dunlap*and*colleagues*(1996)*have*shown*that*use*of*the*standard*effect*size*formula*for*

between_groups*designs*only*very*minimally*affects*the*results,*compared*to*the*corrected*

formula*they*advocate*(their*Equation*3).*We*therefore*used*the*standard*formula*(our*

Equation*1)*for*calculating*effect*sizes*for*repeated_measures*designs.**



Positive+vs.+negative+mean+effect+sizes.+After*calculating*effect*sizes*for*156*

unique*results,*both*positive*(+)*and*negative*(–)*mean*effect*sizes*were*calculated*for*each*

of*the*22*experiments*from*18*studies*(Table*S2).*We*did*not*pool*positive*and*negative*

effect*sizes*together*because*the*dependent*variables*(brain*activation*or*deactivation,*

respectively)*have*no*intrinsic*‘valence’*or*value.*Increased*brain*activity*is*not*necessarily*

‘good’*and*decreased*activity*not*necessarily*‘bad’*–*and*vice*versa.*As*a*result,*pooling*

positive*and*negative*effect*sizes*would*have*had*the*result*that*any*study*reporting*both*

activations*and*deactivations*associated*with*meditation*(of*which*there*were*many)*

would*tend*toward*a*mean*effect*size*of*zero.*This*would*suggest*no*practically*significant*

effects,*an*obviously*unwarranted*interpretation.*The*nature*of*most*functional*

neuroimaging*subtraction*(t_statistic_based)*contrasts*requires*that*activations*and*

deactivations*cannot*both*be*reported*in*exactly*the*same*area*of*the*brain*(although*they*

could*be*proximate):*a*study*reporting*both*positive*and*negative*effects*in*meditation*

practitioners*is*not*suggesting*that*the*overall*effect*of*meditation*approaches*zero*for*a*

given*brain*area.*Rather,*the*results*suggest*that*meditation*leads*to*increased*activation*in*

some*parts*of*the*brain,*and*decreased*activation*in*other*areas*that*are*non8overlapping*

(whether*these*are*distal*or*proximal).*

Mean+effect+size+for+different+meditation+categories.*Combining*mean*effect*sizes*

from*each*experiment,*we*further*calculated*mean*effect*sizes*by*meditation*category*

(focused*attention*vs.*mantra*recitation,*and*so*on)*to*investigate*whether*particular*

meditation*practices*have*differential*effects*on*brain*activation*and/or*deactivation.*In*

line*with*the*recommendations*of*Schmidt*et*al.*(2009),*we*calculated*95%*confidence*



intervals*for*mean*effect*sizes,*to*provide*an*estimate*of*their*precision,*following*

equations*8*and*10*in*Sedlmeier*et*al.*(2012).*

Adjusting+for+inflation+of+effect+sizes+due+to+reporting+of+t?statistics+only+from+

peak+voxels.+Standard*procedure*in*neuroimaging*research*is*to*report!peak*t*or*F*

statistics*only,*which*by*definition*are*the*extreme*(maximum)*values*for*a*given*cluster*of*

significant*difference*between*groups.*Mean*t_statistics*for*an*entire*cluster*of*significant*

differences*are*rarely*reported.*The*effect*sizes*we*calculated*therefore*represent*the*peak,*

maximum*effects*for*each*given*cluster*of*results;*the*actual*mean*t8statistics*for*entire*

clusters*are*necessarily*lower.*Therefore,*our*results*necessarily*overestimate*the*effect*

size*of*the*cluster*as*a*whole.+

In*our*recent*meta_analysis*of*morphometric*neuroimaging*studies*of*meditation,*

we*attempted*to*mitigate*this*inflation*problem*by*examining*a*single*study*in*which*both*

effect*sizes*based*on*peak*t_statistics*and*those*based*on*mean*t8statistics*for*the*entire*

cluster*of*significant*difference*were*reported*(Fox*et*al.,*2014).*This*allowed*us*to*

approximate*the*inflationary*bias*caused*by*reporting*of*only*peak*vs.*entire*clusters*of*t_

statistics,*then*adjust*(deflate)*the*mean*effect*sizes*from*other*studies*accordingly.*We*

found*that*average*cluster*t_statistics*were*about*half*(~57%)*of*the*value*of*the*peak*t_

statistics*for*a*given*cluster*(Fox*et*al.,*2014).**

Unfortunately,*reporting*of*both*peak*and!cluster_wide*t_statistics*is*similarly*rare*

in*functional*neuroimaging*studies*of*meditation.*We*are*aware*of*only*one*study*involving*

meditation*practitioners*that*reports*both*types*of*results*(see*Table*1*in*(Grant*et*al.,*

2011).*This*study*did*not*meet*our*inclusion*criteria,*but*this*was*simply*because*actual*

meditation*practice*(which*we*sought*to*meta_analyze)*was*not*engaged*in*during*MRI*



scanning*(see*Table*S1).*Instead,*putative*trait*differences*in*highly*experienced*

practitioners*were*examined.*That*said,*given*that*this*study*contrasted*experienced*

meditation*practitioners*with*control*subjects,*it*provides*a*starting*point*for*ascertaining*

the*degree*of*inflationary*bias*caused*by*calculating*effect*sizes*solely*from*peak,*rather*

than*average,*t_statistics*for*a*given*cluster.**

Accordingly,*although*we*consider*this*step*absolutely*critical*to*gaining*a*more*

accurate*assessment*of*neuroimaging_related*effect*sizes,*our*only*option*was*to*base*our*

deflationary*adjustment*on*data*from*a*single*study.*The*average*t_statistics*(absolute*

value,*ignoring*sign)*reported*in*the*study*by*Grant*and*colleagues*(2011)*were*2.952*for*

cluster_wide*results*and*4.236*for*maximum*t_statistics*(see*Table*1*in*(Grant*et*al.,*2011).*

These*results*suggest*that*cluster_wide*t_statistics*are*approximately*70%*of*those*

reported*for*maximum*t_statistics*(2.95/4.24*=*0.697),*roughly*in*line*with*our*prior*

efforts*to*deflate*effect*sizes*in*morphometric*investigations*of*meditation*(i.e.,*57%;*(Fox*

et*al.,*2014).*

Assuming*a*roughly*comparable*difference*between*cluster*and*peak*effect*sizes*for*

other*studies,*we*adjusted*all*our*effect*sizes*accordingly,*deflating*them*to*69.7%*of*their*

original*value.*We*readily*acknowledge*the*real*and*significant*limitations*of*this*approach,*

particularly*the*uncertainty*surrounding*the*amount*of*inflation*for*which*adjustment*is*

required.*Whether*our*adjustment*(deflation)*of*effect*sizes*is*too*conservative,*too*lenient,*

or*approximately*accurate,*remains*to*be*seen,*pending*development*of*better*

understanding*of,*and*better*tools*for*assessing,*practical*significance*in*neuroimaging.*For*

present*purposes,*however,*we*considered*this*approach*preferable*to*reporting*effect*

sizes*that*are*guaranteed!to*be*overestimates.*Despite*its*limitations,*our*approach*



provides*a*more*conservative*estimate*of*practical*significance*in*the*functional*

neuroimaging*of*meditation*than*would*be*provided*by*unadjusted*effect*sizes.**

Adjusting+for+inflation+of+effect+sizes+due+to+selective+reporting+of+statistically+

significant+results.+There*have*long*been*serious*and*effective*efforts*to*account*for*Type*I*

statistical*errors*(false*positives)*in*psychological*research*in*general,*as*well*as*in*

neuroimaging*research,*where*massive*numbers*of*multiple*comparisons*(often*thousands*

of*tests)*are*the*norm.*However,*this*sustained*effort*to*control*for*the*rate*of*Type*I*errors*

has*been*paralleled*by*a*serious*failure*to*control*for*the*rate*of*Type*II*errors*(false*

negatives)*–*that*is,*the*chance*of*failing*to*detect*a*true*effect*when*one*is*indeed*present*

(Sedlmeier*and*Gigerenzer,*1989,*Schmidt,*1992).*Among*many*other*concerns,*one*

important*consequence*of*this*situation*is*that*if*results*are*reported*only*when*they*

exceed*a*given*statistical*significance*threshold*(which*is*the*case*in*nearly*all*

psychological*and*neuroscientific*research),*there*will*tend*to*be*a*bias*toward*reporting*of*

effect*sizes*larger*than*the*true*effect*–*and*this*problem*appears*to*be*particularly*true*of*

underpowered*(small*sample)*studies*(Lane*and*Dunlap,*1978,*Kraemer*et*al.,*1998).*This*

is*because*the*initial*criterion*for*publication*and*reporting*(results*exceeding*a*given*

statistical*significance*threshold)*inevitably*leads*to*the*over_reporting*of*larger*group*

differences*that*are*merely*a*result*of*sampling*error*(which*increases*in*smaller*samples)**

–*and*these*apparently*larger*group*differences*will*be*accompanied*by*correspondingly*

large*(and*inflated)*effect*sizes*(Lane*and*Dunlap,*1978,*Schmidt,*1992,*Brand*et*al.,*2008,*

Simonsohn*et*al.,*2014).*

Several*statistical*procedures*have*been*suggested*to*quantitatively*account*for*this*

inflationary*bias,*including*Egger’s*test*(Egger*et*al.,*1997)*and*the*popular*Trim*and*Fill*



method*(Duval*and*Tweedie,*2000b,*a).*However,*more*recent*investigations*suggest*that*

unadjusted*averages*of*effect*size,*as*well*as*the*trim_and_fill*method,*produce*markedly*

inflated*estimates*of*the*true*effect*size*(Simonsohn*et*al.,*2014).*And,*unfortunately,*

methods*such*as*Egger’s*test*(Egger*et*al.,*1997)*or*the*p_curve*method*(Simonsohn*et*al.,*

2014)*rely*critically*on*values*for*the*standard*error,*or*precise*p8values*(respectively)*–*

neither*of*which*is*routinely*reported*in*neuroimaging*studies.*Therefore,*we*addressed*

this*problem*by*employing*a*different*method.*We*deflated*effect*sizes*based*on*the*

general*expected*inflationary*bias*across*study*designs,*as*outlined*in*numerous*

theoretical*and*Monte*Carlo*simulation*studies.*

For*instance,*assume*a*true*effect*size*of*d*=*0.50*(typically*found*in*many*

interventions,*and*considered*‘medium’*size*(Cohen,*1992)),*and*a*significance*threshold*of*

!!=*.05*(which*is*the*threshold*employed*in*virtually*all*of*the*studies*we*examined).*Under*

these*conditions,*and*assuming*a*normal*distribution*of*observed*effects,*then*theoretically*

speaking*the*minimum*effect*size*required*to*attain*significance*is*~0.62,*and*the*average*

of*all*effect*sizes*that*will*be*reported*as*significant*is*~0.89*–*nearly*double*the*true*effect*

size*(Schmidt,*1992).*From*this*theoretical*perspective,*the*true*effect*is*approximately*

56%*the*size*of*the*effects*that*have*are*reported*because*they*exceed*a*given*statistical*

significance*threshold*(Schmidt,*1992).*Recent*years*have*seen*more*comprehensive*

efforts*to*quantify*the*bias*due*to*reporting*of*only*significant*results,*and*have*yielded*

similar*conclusions.*One*study*employing*100,000*Monte*Carlo*simulations*found*that*for*a*

true*effect*of*d*=*0.50,*the*mean*observed*effect*size*(from*significant*results*only)*was*

0.66*–*32%*larger*than*the*true*effect*(Brand*et*al.,*2008).*True*effects,*under*these*

conditions,*are*therefore*approximately*76%*the*size*of*those*that*are*reported.*Although*



this*is*considerably*less*inflation*than*suggested*by*others*(e.g.,*Schmidt,*1992),*these*

authors*assumed*a*total*sample*size*of*N!=*76,*which*is*considerably*larger*than*samples*

employed*in*most*neuroimaging*experiments,*including*the*studies*investigated*here*

(Table*2).*As*already*noted,*this*inflationary*bias*will*tend*to*increase*with*decreasing*

sample*size*(Lane*and*Dunlap,*1978,*Kraemer*et*al.,*1998),*so*the*estimate*of*Brand*et*al.*

(2008)*is*likely*too*lenient*for*our*purposes.*In*a*more*recent*investigation,*simulations*

showed*that*for*a*true*effect*size*of*d*=*0.50*the*average*reported*effect*size*was*around*

0.82–0.85,*depending*on*sample*size*and*whether*fixed_*vs.*random_effects*models*were*

employed*(Simonsohn*et*al.,*2014).*This*corresponds*to*true*effects*that*are*approximately*

60%*the*size*of*those*reported*based*only*on*statistically*significant*results.*

* Importantly,*the*size*of*the*true*effect*has*marked*effects*on*this*bias:*the*difference*

between*true*and*reported*effect*sizes*is*much*greater*for*smaller*true*effects,*and*

becomes*increasingly*negligible*when*true*effects*are*large*(Simonsohn*et*al.,*2014).*For*

purposes*of*our*effect*size*adjustments,*we*assumed*a*‘medium’*effect*size*of*d*=*0.50*and*

employed*the*0.60*ratio*reported*by*Simonsohn*and*colleagues*(2014),*which*appears*to*

us*to*provide*the*most*reliable*and*up_to_date*estimate*of*this*potential*bias.*We*reiterate,*

however,*that*depending*on*the*actual*size*of*the*true*effect,*this*bias*may*be*greater*or*

smaller*than*the*0.60*coefficient*we*employ*here.*Further,*the*adjustments*employed*here*

were*meant*mainly*to*ensure*that*the*conclusions*we*report*do*not*represent*egregiously*

inflated*effect*sizes.*Our*specific*deflation*coefficients*should*be*considered*merely*

preliminary*and*very*much*open*to*amelioration*by*future*empirical,*theoretical,*and*

statistical*simulation*research.**



Further+caveats+regarding+effect+sizes+in+neuroimaging.+Even*given*the*various*

corrections*discussed*above,*another*concern*is*the*interpretation*of*effect*sizes.*The*

interpretive*guidelines*laid*down*by*Cohen*(1992)*were*intended*for*the*behavioral*

sciences,*not*neuroimaging,*and*even*in*the*behavioral*sciences*questions*are*raised*as*to*

their*utility*(Rosenthal,*1996).*Although*it*seems*reasonable*to*use*similar*guidelines*(e.g.,*

the*general*assumption*that*a*one_half*standard*deviation*difference*between*groups*is*

meaningful*and*of*practical*significance),*rigorous*discussion*and*elaboration*of*these*

ideas*has*not*yet*been*undertaken*in*the*field*of*neuroimaging.*Even*in*the*behavioral*and*

social*sciences,*the*interpretation*of*effect*sizes*as*‘small,’*‘medium,’*or*‘large’*is*ultimately*

arbitrary*(Cohen,*1992).*Moreover,*the*true*‘practical’*significance*of*an*effect*depends*on*

many*factors*beyond*magnitude*alone.*Small*effects*can*be*of*large*practical*importance*if*

the*construct*in*question*is*highly*valuable*or*meaningful,*such*as*when*investigating*life_

or_death*outcomes*(Prentice*and*Miller,*1992,*Vacha_Haase*and*Thompson,*2004).*

* Despite*these*limitations,*there*have*already*been*efforts*to*calculate*and*interpret*

effect*sizes*in*meta_analyses*of*neuroimaging*studies*(e.g.,*(Kempton*et*al.,*2008,*Fox*et*al.,*

2014).*The*benefits*of*reporting*effect*size*information*appear*to*greatly*outweigh*the*

drawbacks*inherent*in*their*calculation*and*interpretation*for*neuroimaging*studies.*We*

therefore*calculate*and*report*effect*sizes*here*to*provide*a*general*sense*of*the*magnitude*

of*brain*activation*differences*reported*in*meditation*practitioners,*but*we*emphasize*the*

need*for*caution*in*interpreting*these*results.*

+ +



Supplementary+Results++Table!S1.***Studies*excluded*from*meta_analyses*(N!=*53).*

Study+ Reason+for+exclusion+(Khushu*et*al.,*2000)* Original*publication*not*locatable*(Ueda*et*al.,*2000)* Original*publication*not*locatable*(Bærentsen*et*al.,*2001)* No*voxel*coordinates*reported*(Kjaer*et*al.,*2002)* Only*regions_of_interest*examined;*dopamine*release*measured*(Ritskes*et*al.,*2004)* No*voxel*coordinates*reported*(Kakigi*et*al.,*2005)* Single*subject*case*study*(Khushu*et*al.,*2005)* Original*publication*not*locatable+(Liou*et*al.,*2006)* No*voxel*coordinates*reported*(Orme_Johnson*et*al.,*2006)* No*voxel*coordinates*reported*(Creswell*et*al.,*2007)* No*meditators*involved;*only*'dispositional'*mindfulness*scored*(Holzel*et*al.,*2007)* Only*regions_of_interest*examined*(Kozasa*et*al.,*2008)* No*voxel*coordinates*reported*(Pagnoni*et*al.,*2008)* Only*regions_of_interest*investigated*(for*contrast*of*interest)*(Beauregard*et*al.,*2009)* Meditation*experience*ambiguous*(Baerentsen*et*al.,*2010)* Multiple*meditation*types*pooled*in*analysis*(Engström*and*Söderfeldt,*2010)* Single*subject*case*study;*no*voxel*coordinates*reported*(Farb*et*al.,*2010)* No*actual*meditation*engaged*in*during*scanning*(Goldin*and*Gross,*2010)* Clinical*population*(social*anxiety*disorder)*(Short*et*al.,*2010)* No*voxel*coordinates*reported*(Grant*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Jang*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Josipovic*et*al.,*2011)* Only*regions_of_interest*examined*(Kilpatrick*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Kirk*et*al.,*2011)* No*actual*meditation*engaged*in*during*scanning*(Xue*et*al.,*2011)* No*voxel*coordinates*reported*(Zeidan*et*al.,*2011)* No*voxel*coordinates*reported*(Allen*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Desbordes*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Froeliger*et*al.,*2012a)* No*voxel*coordinates*reported*(Froeliger*et*al.,*2012b)* No*actual*meditation*engaged*in*during*scanning*(Hasenkamp*and*Barsalou,*2012)* No*actual*meditation*engaged*in*during*scanning*(Klimecki*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Kozasa*et*al.,*2012)* No*actual*meditation*engaged*in*during*scanning*(Monti*et*al.,*2012)* Clinical*population*(breast*cancer)*(Pagnoni,*2012)* Only*differences*in*skewness*of*fMRI*signal*reported*(Garrison*et*al.,*2013a)* No*voxel*coordinates*reported*(Garrison*et*al.,*2013b)* No*voxel*coordinates*reported*(Goldin*et*al.,*2013)* Clinical*population*(social*anxiety*disorder)*(Hagerty*et*al.,*2013)* Single*subject*case*study*(Ives_Deliperi*et*al.,*2013)* Clinical*population*(bipolar*disorder)*(Klimecki*et*al.,*2013)* No*actual*meditation*engaged*in*during*scanning*(Mascaro*et*al.,*2013a)* No*actual*meditation*engaged*in*during*scanning*(Mascaro*et*al.,*2013b)* No*actual*meditation*engaged*in*during*scanning*(Paul*et*al.,*2013)* No*meditators*involved;*only*trait*mindfulness*scored*(Prakash*et*al.,*2013)* No*meditators*involved;*only*trait*mindfulness*scored*(Taylor*et*al.,*2013)* No*actual*meditation*engaged*in*during*scanning*(Wells*et*al.,*2013)* Clinical*population*(mild*cognitive*impairment)*(Westbrook*et*al.,*2013)* Quasi_clinical*population*(abstinent/craving*smokers)*(Zeidan*et*al.,*2013)* No*voxel*coordinates*reported*(Garrison*et*al.,*2014)* No*voxel*coordinates*reported*(for*contrast*of*interest)*(Kirk*et*al.,*2014)* No*actual*meditation*engaged*in*during*scanning;*meditation*style*not*reported*(Josipovic,*2014)* No*voxel*coordinates*reported;*preliminary*data*only*(Ding*et*al.,*2015)* No*actual*meditation*engaged*in*during*scanning*



Table!S2.!!*Supplementary*meta_analysis*of*focused*attention*meditation*(excluding*studies*

involving*short_term*meditation*training).*



Peak+ALE+value+

Activations+


Dorsal*anterior*cingulate*cortex* 304* M* 2,*12,*32*(BA*24)* 0.0112*

Deactivations+

Posterior*cingulate*cortex* 152* M* _6,*_60,*18*(BA*30)* 0.0071*

Inferior*parietal*lobule* 144* L* _48,*_72,*30*(BA*39)* 0.0071*

!**

*! !



Table!S3.!!*Supplementary*meta_analysis*of*mantra*recitation*meditation*(excluding*studies*




Peak+ALE+value+

Activations+

Premotor*cortex* 896* L* _30,4,*60*(BA*6)* 0.0137*

Supplementary*motor*area*584* M* 0,*12,*54*(BA*6)* 0.0111*

112* M* _4,*2,*68*(BA*6)* 0.0080*

Putamen/Lateral*globus*pallidus* 368* R* 28,*_16,*_6* 0.0111*

Fusiform*gyrus* 248* R* 40,*_26,*_30*(BA*20/36)* 0.0093*

Cuneus* 160* R* 24,*_86,*26*(BA*18)* 0.0082*

Precuneus* 152* L* _14,*_56,*54*(BA*7)* 0.0082*

*!**! !



Table!S4.!!*Supplementary*meta_analysis*of*open*monitoring*meditation*(excluding*studies*




Peak+ALE+value+

Activations+

Temporopolar*cortex* 160* L* _45,*19,*_30*(BA*38)* 0.0075*

Insular*cortex*(mid/posterior)* 160* R* 45,*_20,*13*(BA*13)* 0.0075*

Pre_supplementary*motor*area* 152* M* 0,*8,*64*(BA*6)* 0.0080*

Deactivations*

Thalamus*(pulvinar)*128* R* 17,*_24,*10* 0.0084*

112* R* 17,*_30,*4* 0.0083*

Parahippocampus* 104* R* 24,*_32,*_9*(BA*27/35)* 0.0086*

* !



Table!S5.***Supplementary*meta_analysis*of*loving_kindness/compassion*meditation*

(excluding*studies*involving*short_term*meditation*training).*



Peak+ALE+value+

Activations+

Anterior*insula* 632* R* 38,*22,*14*(BA*13)* 0.0135*

Parieto_occipital*sulcus* 376* R* 24,*_60,*18*(BA*23/31)* 0.0115*

Somatosensory*cortices/Inferior*parietal*lobule* 376* R* 54,*_26,*30*(BA*2/40)* 0.0101*

Postcentral*gyrus/*Somatosensory*cortex* 104* L* _60,*_8,*20* 0.0083*

!**+ +



Supplementary+Discussion+

*

Functional!neuroanatomy!of!focused!attention!meditation.!

Activations.+If*focused*attention*meditation*so*often*involves*strong*focus*on*a*

visual*stimulus*or*the*interoceptive*signals*associated*with*respiration,*why*were*

activations*not*observed*in*visual*or*interoceptive*cortices?*Small*(non_significant)*clusters*

of*activation*were*in*fact*observed*in*the*lateral*geniculate*nucleus*of*the*thalamus,*which*

processes*and*relays*visual*information*(Casagrande*and*Norton,*1991),*as*well*as*in*the*

left*insula,*a*major*center*for*interoceptive*information*processing*(Critchley*et*al.,*2004,*

Craig,*2009,*Farb*et*al.,*2013a).*These*clusters*can*be*seen*in*the*detailed*supplementary*

data*on*focused*attention*meditation*(Fig.*S1).*One*reason*these*clusters*may*not*have*

been*larger*is*due*to*the*heterogeneity*of*the*studies*included*in*the*meta_analysis.*That*is,*

whereas*effortful*cognitive*control*along*with*attention*to*and*suppression*of*internal*

thought*streams*were*likely*common*across*these*studies,*activations*related*to*the*

particular*object*of*attentional*focus*may*have*been*too*disparate*to*attain*meta_analytic*

significance.*

Deactivations.+The*specific*role*of*the*posterior*cingulate*cortex*in*meditation*has*

been*explored*more*extensively*in*a*recent*study*examining*practitioners*from*diverse*

contemplative*backgrounds*(a*mix*of*Zen,*Catholic,*Theravada*Buddhist,*and*Tibetan*

Buddhist*practitioners).*Participants*engaged*in*a*focused*attention*meditation*where*the*

object*of*focus*was*the*breath*(Garrison*et*al.,*2013a).*Following*an*fMRI*scan,*participants*

described*the*subjective*qualities*of*their*meditation*that*corresponded*to*a*feedback*

graph*depicting*the*time*course*of*activity*from*their*posterior*cingulate*cortex*throughout*



the*scan.*It*was*found*that*deactivation!of*the*posterior*cingulate*cortex*was*associated*

with*qualities*of*meditation*described*by*terms*such*as*‘concentration’*or*‘undistracted*

awareness’*(Garrison*et*al.,*2013a).*The*converse*was*also*true:*activation*of*posterior*

cingulate*cortex*was*associated*with*subjective*distraction*and*poor*quality*of*focus*during*

meditation*(described,*e.g.,*as*‘distraction’*or*‘distracted*awareness’)*(Garrison*et*al.,*

2013a).*Another*study*from*the*same*group*reported*similar*findings*(Garrison*et*al.,*

2013b),*which*are*in*line*with*our*meta_analytic*results.*

*

Functional!neuroanatomy!of!mantra!recitation!meditation!

Activations.+Activations*were*also*observed*in*the*fusiform*gyrus*(BA*20),*cuneus,*

and*the*anterior*precuneus*(BA*7),*in*a*location*almost*identical*to*a*cluster*observed*in*

our*recent*meta_analysis*of*brain*structure*differences*in*experienced*meditation*

practitioners*(see*Fig.*2g*in*(Fox*et*al.,*2014).*Both*clusters*were*observed*in*a*putative*

‘anterior’*subregion*of*the*precuneus*with*strong*connections*to*somatomotor*cortices*and*

insula,*which*may*play*a*role*in*coordination*of*motor*behavior*as*well*as*the*generation*of*

motor*imagery*(Hanakawa*et*al.,*2003,*Malouin*et*al.,*2003,*Cavanna*and*Trimble,*2006).*A*

speculative*role*for*anterior*precuneus,*then,*may*be*in*assisting*in*the*overt*or*mental*

repetition*of*the*mantra.*Alternatively,*or*in*addition*to*this*interpretation,*the*activation*of*

the*precuneus*as*well*as*the*fusiform*gyrus*and*cuneus*may*indicate*that*practitioners*

evoke*visual*imagery*along*with*mantra*repetition.*Detailed*subjective*reports*will*be*

necessary*to*more*fully*elucidate*the*processes*activated*during*mantra*recitation,*and*by*

extension*the*meaning*of*these*activations.**

+



Functional!neuroanatomy!of!open!monitoring!meditation.!

Deactivations.+Many*other*smaller*(non_significant)*clusters*of*deactivation*were*

observed.*One*deactivation*that*accords*well*with*the*goal*of*open*monitoring*meditation*

was*located*in*the+rostromedial*prefrontal*cortex*(medial*BA*10)*–*as*opposed*to*the*

cluster*of*activation*observed*in*lateral*BA*10*(see*Fig.*S3).*A*central*goal*of*open*

monitoring*is*to*dampen*the*tendency*to*become*ensnared*in*one’s*thoughts*and*emotions,*

and*to*not*turn*isolated*mental*content*into*extended*streams*of*self_referential*thinking*

(Goenka,*2000).*As*medial*prefrontal*cortex*has*been*so*consistently*implicated*in*these*

kinds*of*mind_wandering*(Fox*et*al.,*2015)*and*self_referential*thought*(Northoff*et*al.,*

2006),*a*simple*explanation*is*that*its*deactivation*represents*the*successful*execution*of*

open*monitoring*(Farb*et*al.,*2007).**

Consistent*with*this*explanation*are*other*small*(non_significant)*clusters*of*

deactivation*observed*bilaterally*in*the*subgenual*anterior*cingulate*cortex*(or*

ventromedial*prefrontal*cortex;*BA*25)*and*bilaterally*in*the*medial*temporal*lobe*(BAs*27,*

28,*and*36,*including*the*hippocampus)*–*both*of*which*are*similarly*implicated*in*the*

default*mode*network*(Buckner*et*al.,*2008)*as*well*as*mind_wandering*and*related*

spontaneous*thought*processes*(Fox*et*al.,*2015).*Also*consistent*with*such*an*

interpretation*were*small*clusters*of*deactivation*bilaterally*in*the*posterior*cingulate*

cortex*(BAs*23,*29,*30,*and*31),*likewise*involved*in*the*default*mode*network*(Buckner*et*

al.,*2008)*and*mind_wandering*(Fox*et*al.,*2015).*All*of*these*regions*of*course*play*many*

other*roles,*but*nonetheless*the*widespread*deactivation*of*so*many*important*default*

network*hubs,*which*are*consistently*activated*during*mind_wandering*(Fox*et*al.,*2015),*

is*suggestive*of*a*lowered*frequency*of,*and/or*a*decreased*involvement*in,*one’s*thoughts.*



Various*other*small*clusters*of*deactivation*were*also*observed,*for*instance*in*the*

left*lingual*gyrus*of*the*occipital*lobe*(BA*18/19).*We*have*previously*found*the*lingual*

gyrus*to*be*consistently*recruited*during*both*nighttime*dreaming*(Fox*et*al.,*2013)*and*

waking*daydreaming/mind_wandering*(Domhoff*and*Fox,*2015,*Fox*et*al.,*2015),*and*

lesions*to*this*region*eliminate*all*visual*imagery*in*dreams,*while*sparing*the*dream*

experience*itself*(Solms,*1997).*In*line*with*our*suggestions*regarding*deactivation*of*

default*network*areas,*it*may*be*that*open*monitoring*dampens*the*visual*imagery*so*

characteristic*of*mind_wandering*during*normal*waking*(Fox*et*al.,*2013),*as*well*as*during*

formal*meditation*practice*(Austin,*1999).*

*

Functional!neuroanatomy!of!loving8kindness!and!compassion!meditation!

Activations.*A*notable*but*non_significant*cluster*of*activation*was*observed*in*the*

anterior*cingulate*cortex*(BA*24),*very*near*to*a*meta_analytic*cluster*reported*in*a*meta_

analysis*of*empathy*for*the*pain*of*others*(see*Fig.*2*in*(Lamm*et*al.,*2011)).*This*cluster*

was*located*in*a*more*anterior*location*than*those*identified*in*the*other*types*of*

meditation.*As*with*somatosensory*cortices*and*inferior*parietal*lobule*(discussed*above),*

this*area*is*also*consistently*implicated*in*pain*perception,*particularly*its*affective*(as*

opposed*to*sensory)*component*(Grant*et*al.,*2011).*Similarly,*then,*this*area*might*play*

overlapping*roles*in*imagining*the*pain*and*distress*of*others,*as*well*as*empathizing*with*

their*pain*and*distress.*

Deactivations.+No*significant*deactivations*were*observed,*and*very*few*non_

significant*deactivations*were*apparent*(Fig.*S4).*As*noted*above,*however,*our*meta_

analysis*of*loving_kindness*and*compassion*meditations*was*based*on*the*fewest*



experiments*and*smallest*number*of*foci*(Table*1),*and*therefore*had*lower*statistical*

power*than*the*other*meta_analyses.*The*relative*lack*of*activations*and*deactivations*in*

this*form*of*meditation*practice*more*likely*reflects*this*meta_analytic*limitation*rather*

than*any*inherent*feature*of*the*practice*itself.*More*research*is*therefore*needed*to*better*

illuminate*the*activations*and*deactivations*associated*with*this*group*of*meditation*

practices.!

!

Convergent!findings!across!meditation!categories*

+ Insula.*The*relatively*stronger*(and*statistically*significant)*recruitment*of*the*

insula*in*open*monitoring*and*loving_kindness/compassion*meditation*is*further*

consistent*with*the*character*of*these*practices.*These*practices*tend*to*focus*heavily*on*

awareness*of*the*body*and*emotions*(open*monitoring),*or*empathy,*mentalizing,*and*

perspective_taking*(loving_kindness/compassion).*For*open*monitoring,*there*is*growing*

evidence*that*practitioners*who*heavily*emphasize*this*practice*show*heightened*

interoceptive*and*exteroceptive*bodily*awareness.*Support*for*this*enhanced*awareness*

comes*from*multiple*methodologies,*including*behavioral*(Fox*et*al.,*2012),*physiological*

(Sze*et*al.,*2010),*magnetoencephalographic*(Kerr*et*al.,*2013),*and*fMRI*(Farb*et*al.,*2007,*

Farb*et*al.,*2013b)*research.*

Beyond*body*awareness*and*interoception,*the*insula*is*also*reliably*implicated*in*

empathy*and*the*perspective_taking*or*mentalizing*that*empathy*often*entails*(Lamm*et*al.,*

2011,*Bernhardt*and*Singer,*2012).*The*significant*insula*cluster*observed*in*loving_

kindness*and*compassion*meditation,*then,*suggests*an*alternate*function*that*the*insula*



might*serve*in*meditations*involving*empathy,*imaging*the*pain*and*suffering*of*others,*

and*the*cultivation*of*compassionate*and*prosocial*responses*to*this*distress.*

Although*further*speculation*about*the*insula’s*particular*function(s)*across*various*

types*of*meditation*seems*unwarranted*at*this*early*stage,*both*morphometric*meta_

analysis*(Fox*et*al.,*2014)*and*the*present*functional*meta_analysis*agree*that*it*plays*an*

important*role*across*several*forms*of*meditation*practice.*

*

!

!

Are!contemplative!practices!dissociable!by!electrophysiological!and!neurochemical!measures?*

One*group*has*attempted*to*integrate*EEG*findings*from*across*many*meditation*

styles,*and*similar*to*our*claims*here,*argued*that*various*forms*of*meditation*are*

preferentially*associated*with*differing*electrical*rhythms*in*the*brain*(e.g.,*theta,*beta,*

gamma,*and*so*on)*(Travis*and*Shear,*2010).*Others,*however,*have*suggested*major*

commonalities*in*EEG*signatures*across*many*different*meditation*styles*(Lehmann*et*al.,*

2012).*Whether*these*findings*can*be*integrated*with*the*current*arguments*from*blood_

flow*or*blood_oxygenation_dependent*measures*remains*an*important*question*for*future*

research*and*meta_analytic*synthesis.*

The*ability*of*positron*emission*tomography*(PET)*scanners*to*investigate*the*

activity*of*particular*neurotransmitters*and*neuromodulators*has*hardly*been*exploited*in*

meditation*research.*A*single*study*examining*yoga!nidra*using*PET*has*reported*increased*

dopamine*release*during*this*form*of*practice*(Kjaer*et*al.,*2002),*but*to*our*knowledge*no*

research*has*followed*up*on*these*initial*findings.*Various*meditation*practices*consistently*



lead*to*subjective*changes*in*relaxation,*levels*of*alertness*and*vigilance,*engagement*in*

visionary*and*dream_like*experiences,*and*so*on*–*all*of*which*are*known*to*be*heavily*

driven*by*changes*in*levels*of*various*neurotransmitters*and*neuromodulators*(Perry*et*al.,*

2002).*As*such,*there*is*good*reason*to*believe*that*both*the*tonic*and*phasic*activity*

profiles*of*various*neurotransmitters*might*vary*markedly*across*different*practice*

categories.*Given*the*paucity*of*research*to*date,*however,*these*remain*open*questions*to*

be*addressed*by*future*research.*

*

!

!

Other!methodological!challenges!in!the!neuroimaging!of!meditation*

‘Overshadowing.’+As*discussed*in*the*Introduction,*we*assumed*a*one8to8many*

logical*relationship*(Coombs*et*al.,*1970,*Cacioppo*and*Tassinary,*1990)*between*a*given*

psychological*meditation*state*(Ψ)*and*its*diverse*neural*correlates*(Φ):*one*form*of*

meditation*practice*(e.g.,*focused*attention)*would*be*accompanied*by*numerous*(many)*

but*hypothetically*consistent*neurophysiological*responses.*If*a*given*meditation*state*is*

strongly*colored*by*a*practitioner’s*contemplative*background*(experience*with*a*variety*

of*other*meditation*techniques),*however,*then*this*assumption*no*longer*holds,*and*the*

relationship*assumes*a*many8to8many*form,*making*it*much*more*difficult*to*draw*any*

reliable*conclusions.**

Unfortunately,*it*seems*likely*that*this*is*the*situation*in*at*least*some*of*our*sample:*

as*already*noted*(Table*1),*some*investigators*had*the*same*sample*of*practitioners*engage*

in*multiple*meditation*techniques*in*the*same*study.*This*was*possible*because*many*



practitioners*are*familiar*with,*and*have*long*practiced,*multiple*techniques.*Clearly,*the*

particular*ratio*of*experience*with*different*techniques*will*vary*among*individual*

practitioners,*and/or*practitioners*from*differing*meditation*traditions,*adding*an*

additional*(and*unknown)*degree*of*heterogeneity.*For*instance,*some*traditions*focus*

heavily*on*mantra*meditation*practice*(e.g.,*Transcendental*Meditation),*although*their*

practitioners*may*of*course*also*be*familiar*with*other*practices.*Other*traditions*(e.g.,*

Theravada*Buddhist)*tend*to*focus*more*on*open*monitoring*techniques.*The*central*point*

is*that*these*various*emphases*are*largely*unknown.*When*a*practitioner*participates*in*a*

neuroimaging*study*and*is*asked*to*engage*in*a*particular*practice*for*a*short*period*of*

time*(usually*only*a*few*minutes)*in*a*brain*scanner,*their*traditional*contemplative*

background*and*the*emphasis*they*have*placed*on*various*techniques*over*their*years*of*

practice*may*greatly*influence*their*manner*of*meditation*practice*(and*the*concomitant*

neural*correlates*investigators*record*and*report)*–*but*these*diverse*contemplative*

backgrounds*are*rarely*investigated*or*reported*(typically,*total*hours*or*years*of*

meditation*experience*is*the*only*data*collected).*Although*total*hours*of*experience*is*a*

useful*preliminary*measure,*the*incredible*diversity*of*meditation*techniques*clearly*calls*

for*more*detailed*measures*in*future*work.*

Integration+of+functional+neuroimaging+methods+with+behavioral+measures.+In*

our*previous*meta_analysis,*we*noted*that*numerous*studies*attempted*to*directly*link*

brain*structure*changes*to*behavior*change*or*scores*on*various*self_report*measures,*but*

almost*all*of*the*reported*correlations*were*statistically*marginal*and/or*statistically*non_

independent.*Among*the*present*pool*of*studies,*a*few*have*reported*modest*correlations*

between*meditation*expertise*(i.e.,*total*hours*of*practice)*and*differences*in*brain*



activation*during*a*given*meditation*state*(e.g.,*(Lazar*et*al.,*2000,*Brefczynski_Lewis*et*al.,*

2007,*Farb*et*al.,*2013b).*Few,*however,*have*related*brain*activation*differences*during!

meditation*states*to*actual*behavior,*or*even*to*self_report*questionnaires*(e.g.,*for*anxiety*

or*mindfulness):*of*the*26*studies*included*here,*only*four*correlated*their*findings*with*

behavioral*outcomes*other*than*meditation*experience*or*expertise.*We*acknowledge*that*

this*is*an*extremely*challenging*problem:*of*innumerable*potential*outcomes,*what*

behavior*should*be*measured?*What*self_report*questionnaires*should*be*considered*the*

most*relevant*and*reliable?*Can*reliable*correlations*be*obtained*with*the*small*samples*

typical*of*neuroimaging*studies?*Is*activation*during!the*meditation*state*even*the*relevant*

independent*variable*–*i.e.,*should*these*correlations*instead*be*sought*using*baseline,*trait!

levels*of*brain*activity,*outside*of*the*meditation*practice*itself*(see*5.12.4)?**

* As*noted*above,*however,*several*of*the*more*recent*fMRI*studies*have*attempted*to*

integrate*neuroimaging*findings*with*behavioral*measures*other*than*just*meditation*

experience*itself*(Lee*et*al.,*2012,*Lutz*et*al.,*2013,*Weng*et*al.,*2013,*Lutz*et*al.,*2014).*For*

instance,*Weng*et*al.*(2013),*in*a*study*of*compassion*meditation,*reported*that*those*with*

greater*brain*activation*in*dorsolateral*prefrontal*cortex*and*inferior*parietal*cortex*during*

the*meditation*were*more*likely*to*redistribute*funds*more*equitably*in*an*economic*game*

they*subsequently*participated*in.*This*study*therefore*demonstrated*not*only*that*

compassion*meditation*training*leads*to*differential*neural*responses*to*the*suffering*of*

others*and*to*increased*altruistic*behaviors*in*an*economic*game*–*it*also*linked*these*

findings*together,*providing*evidence*that*specific*contemplative*training*leads*to*changes*

in*brain*activity*changes*which*in*turn*are*related*to*meaningful*behavioral*outcomes.*This*

multifaceted*approach*remains*rare,*but*provides*a*model*for*future*research,*which*can*



(and*should)*integrate*neuroimaging*measures*with*behavioral*and*first_person*report*

outcomes.+

Further,*several*of*the*studies*excluded*from*our*meta_analysis*that*examined*‘trait’*

differences*in*meditators*(Table*S1)*or*that*employed*meditation*in*clinical*populations*

have*also*assessed*various*outcome*measures*as*correlated*with*their*neuroimaging*

results*(Table*S1).*However,*we*hasten*to*reiterate*the*caveats*we*have*raised*before*

regarding*such*correlational*analyses*(cf.*Fox*et*al.,*2014):*for*instance,*correlation*

coefficients*are*highly*unstable*with*small*sample*sizes*(Glass*and*Hopkins,*1970),*and*

efforts*to*correlate*neuroimaging*findings*with*behavioral*measures*are*highly*susceptible*

to*‘circular’*or*non_independent*analysis,*which*can*grossly*inflate*correlation*coefficients*

(Vul*et*al.,*2009,*Hupé,*2015).*Nonetheless,*in*order*for*the*neuroimaging*of*meditation*to*

move*beyond*cartography*of*brain*activation*differences*and*toward*an*integrative*science*

linking*psychological*training*with*brain*and*behavior,*these*methodological*and*statistical*

difficulties*will*need*to*be*overcome.*

**+ +



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Figure!S1.***Activations*and*deactivations*associated*with*focused*attention*mediation.**

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Figure!S2.***Activations*and*deactivations*associated*with*mantra*recitation*mediation.**

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Figure!S3.***Activations*and*deactivations*associated*with*open*monitoring*mediation.**

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Figure!S4.***Activations*associated*with*loving_kindness*and*compassion*mediation.**

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