Auditory Processing & Tinnitus
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Transcript of Auditory Processing & Tinnitus
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Auditory Processing & Tinnitus!
Wesley Jackson
A neural enthusiasts primer to
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Some simple physics.! Although soundis a perceptual experience, any sound can
be physically modeled as a specific waveform.!
Intro!
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Some simple physics.! Although soundis a perceptual experience, any sound can
be physically modeled as a specific waveform.!
Asinetoneisthesimplestsound,
consis1ngofasinglefrequency
component(Hz)ofagiven
amplitude(dB).
(sinetonesandothersuch
simplesoundsmaycorrelate
withhighlevelsofnostalgia)
Intro!
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Some simple physics.! Although soundis a perceptual experience, any sound can
be physically modeled as a specific waveform.!
Asinetoneisthesimplestsound,
consis1ngofasinglefrequency
component(Hz)ofagiven
amplitude(dB).
Naturalsoundstendtobecomplex
(consis1ngofmanyfrequency
components).
TheyconsistofpaCernsofchangesin
airpressure.
Intro!
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TheauditorysystemtranslatesthesepaCernsofairpressurechangeintopaCernsofneuronalfiring.
Intro!
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PeripheralAuditorySystem
Auditory
processing
beginsin
cochlea
The Auditory System!
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Auditory
informa1onis
senttothebrain
bytheauditorynerves.
The Auditory System!PeripheralAuditorySystem
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Sound waves are translated into nerve impulses!ochlea
Specificacous1cfrequenciescause
certainloca1onsalongthebasilar
membranetovibrate.
Tonotopicorganiza5onofthebasilarmembrane.
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Sound waves are translated into nerve impulses!)Innerearhaircellsaredeflectedby
vibra1onsalongthebasilarmembrane
ands1mulateauditorynervesbydepolarizingafferentnervecells.
2)Becausethebasilarmembraneis
tonotopicallyorganized,theauditory
nervesencodespecificfrequencies.
NS
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frequency encoding?!Anauditorynervesfiringratewillpeakatsomespecific
characteris5cfrequency(CF).
TheFwillhavealowresponsethreshold;rela1velylow
acous1cenergy(amplitude)isrequiredforaresponse.
Ac1vity(firingrate)peaksatF
LowestdBthresholdatF
FREQUENY (KHZ)!
a.Measuring
peakresponse
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frequency encoding?!TherangeofresponsesasFisapproachedistherecep5vefield.
Seehowthispar1cularfrequency
takesthelowestdBtoevokea
response?Thisisthiscells
characteris5cfrequency!
Manycellswithdifferent
Fsencode
thefull
acous1c
frequency
spectrum.
Itsrecep5vefieldistheshapeof
theresponseacrossmany
frequencies.
b.Measuring
amplitude
threshold
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encoded acoustic information sent to CNS:brainstem.!
PNS NS
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entralAuditorySystem
The Auditory System!
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entralNervousSystem(NS)
BRAINSTEM
Hearingcanbetestedbymeasuringthe
brainstemsresponsetosoundsofvariousfrequenciesandamplitudes
AuditoryBrainstemResponse(ABR)
Whatisthe
minimumdB
threshold(i.e.
hearingthreshold)
forsucha
response?
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entralNervousSystem(NS)
THALAMUS
MedialGeniculateBody(MGB)
PrimaryAuditoryortex(AI)
I
II
III
IV
V
VI
or1calLayers*
Cor3calLayersIII/IV:
25%GABAergic
interneurons
Thalamicinput
Projecttoother
cor1callayers
*No5cethecolumnarorganiza5on!
Thesecolumnsprocesssimilar
acous5cproper5es.
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GABAergic interneurons!GABA*istheprimaryinhibitory
neurotransmiCer.
.ItissynthesizedfromtheexcitatoryneurotransmiCerglutamatebytheenzyme
glutamicaciddecarboxylase(GAD).
GAD65GABAglutamate
Wearepar1cularlyinterestedinthe
expressionofGAD65.Why?Because
manipula1ngtheexpressionofGAD67can
belethal!
*GABAisnottobe
confusedwiththe80ssupergroup.
Transcrip3onfactorsregulategeneexpression
2.GADisproducedbyGABAergic
interneurons,whosedevelopment
dependsonDlxtranscrip5onfactors
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PV+ GABAergic interneuronsin cortical layers III/IV!
Basketcells
MostcommoninhibitoryneuroninAI
Projecttosoma(cellbody)ofpyramidalneurons
Thesecellscommonlyexpressthe
proteinparvalbumin&arethuscalled
PV+BasketCells(PV-B).
Interneuronsprovidelocal
connec1onswithincortexandare
primarilyinhibitory(GABAergic)
Winer&Schreiner(2011).TheAuditoryCortex
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PrimaryAuditoryortex(AI)
AuditoryPathwayOverview
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Hearing Damage!
Damagedhaircellsnolongerrespond
toenvironmentalfrequencies.
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Hearing Damage!. Haircellsresponsivetohigher
frequenciesarentasresponsiveas
before.
2. Thismeanstherewillbelessthalamicinputtothecortexforthesefrequencies.
3. Socor1calneuronstunedtothesefrequencieswillhavereduced
thalamicinputandbecome
deafferented;theynowprimarily
respondtolowerfrequenciesthan
before.
(Yangetal.2011)
Seehowhighfrequencythresholdsdontrecovera[erhearingdamage?
ABRshowsimpairedhigh-frequency
hearingaerhearingdamage:
Socor3calresponseemphasizes
lowerfrequencies:
Eff f A di D ff i
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S
Effects of Auditory Deafferentation:1) Cortical Reorganization& Map Disruption!
Sensory deafferentation causes many changes to the Central Nervous System!Thetonotopicorganiza1onofAIbecomes
reorganizedasneuronsnowrespondprimarily
tolowerfrequencysoundsthanbeforehearing
damage.
)ThisneuronpreviouslyhadaclearhighF
2)Nolongersopreciselytunedfor
(previously)highfrequencyneurons!
Hencethemapdisrup1on
(Yangetal.2011)
Seehowthehigh
frequencyareaofthe
cortexisnolonger
tonotopically
organizedaer
hearingdamage?
Thisisanexampleof
mapdisrup5on!
Eff t f A dit D ff t ti
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Effects of Auditory Deafferentation:2) Morphological Changes!
Sensory deafferentation causes many changes to the Central Nervous System!or1calmapdisrup1onisaccompaniedbymorphological
changestodeafferentedpyramidalneurons.
Eff f A di D ff i
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Effects of Auditory Deafferentation:3) Changes in Synaptic Plasticity!
Sensory deafferentation causes many changes to the Central Nervous System!Deafferentedneuronsdontfireasoenbecause
theyhavelostmuchthalamicinput.
Therefore,tomaintainoveralllevelsofexcitability,
tonicinhibi3onisreducedbydecreasinglevelsof
ambientGABA.Thisisachievedbydownregula1onofGAD.
WheredidalltheGADgo?
(Yangetal.2011)
Eff f A di D ff i
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Effects of Auditory Deafferentation:3) Changes in Synaptic Plasticity!
Sensory deafferentation causes many changes to the Central Nervous System!Tonicinhibi3oniscausedbyambientGABA
extrasynap1cGABAwhich
modulatesbaseline
neuronalexcitability.Extrasynap5cmeansfar
fromthesynapses.
RememberhowGABAergic
basketcellssynapsetothe
somaofpyramidalneurons,
ratherthanthedendrites?
Eff f A di D ff i
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Effects of Auditory Deafferentation:4) Tinnitus!!
Sensory deafferentation causes many changes to the Central Nervous System!Thisdeafferenta3on-mo3vatedincreaseinexcitabilityisthemost
likelycauseof3nnitus,astheseoverexcitedhighCFneuronswillnowfireveryoen!
Otherneuronslisteningtotheac3vityoftheseneuronswillinterpret
thisincreaseinac3vityasthepresenceofthatfrequencyinthe
environmenthencethepercep3onofsound,or3nnitus!
Note:ContrarytoGoogleimagesearch,theaboveresponseisnotactuallyareliable
characteris5cbehavioralcorrelateof5nnitus.
Eff t f A dit D ff t ti
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Effects of Auditory Deafferentation:4) Tinnitus!!
Sensory deafferentation causes many changes to the Central Nervous System!Thisdeafferenta3on-mo3vatedincreaseinexcitabilityisthemost
likelycauseof3nnitus,astheseoverexcitedhighCFneuronswillnowfireveryoen!
Otherneuronslisteningtotheac3vityoftheseneuronswillinterpret
thisincreaseinac3vityasthepresenceofthatfrequencyinthe
environmenthencethepercep3onofsound,or3nnitus!
Note:ContrarytoGoogleimagesearch,theaboveresponseisnotactuallyareliable
characteris5cbehavioralcorrelateof5nnitus.