Right Brain Left BrainPsych 546-01

Dr David A Kaiser

Syllabus

LECTURE 1History of Laterality

Neolithic Neurology

(i.e. trephination)

Corpus Callosum

Plato Aristotle (427-347) (384-322)

Aristotle: Right side is the origin of motion in all creatures (he was an exception, a left-hander)

Plato favored symmetry

Andreas Vesalius(1514-1564)

De Humani Corporis Fabrica (The Fabric of The Human Body) – 1543

Studied anatomy solely for structure

Cerebral Symmetry: Bichat

• Argued for general law of symmetry

• Symmetrical functioning between paired organs necessary because one had to be able to relate to the external world equally with both sides of body (1805).

Helped found Science of Histology

Francois X. Bichat (1771-1802)

Cerebral Localization (Mosaic): Franz Gall

• Phrenology: Analysis of shapes and lumps of skull reveals personality and intellect.

• Identified 27 major faculties like imitation, spirituality

Franz Joseph Gall (1758-1828)

•Noticed how verbally superior schoolmates had bulging eyes, and believed language abilities resided behind eyes (suborbital region of frontal lobe), overdeveloped in these few

Cerebral Holism (Diffuse representation – Equipotentiality)

• Pierre Flourens (1824) set up lab to attack Gall’s mind-brain equivalence, the materialistic heresies which undermined the unity of the soul, human immortality, free will, and the very existence of God

• He demonstrated that main divisions of brain were responsible for largely different functions.

• By removing cerebrum, all perceptions, motor function, and judgment were abolished.

• Removal of cerebellum affected equilibrium and motor coordination.

• Destruction of brain stem caused death.

• Extensive and indiscriminate cortical lesions in birds and rabbits showed little behavioral change, which led him to believe that these functions are represented diffusely around the brain.

Cerebral Localization: BouillaudVocal supporter of Gall and his theory

of brain as plurality of organs.

Bouillaud was “the soul of the doctrine of localization” for 50 years.

From 1825 to 1860 he defended Gall in debates before French Academie de Medecine

Localization remained highly polarizing - Mind has many faculties but brain must be unitary for soul to enter- Language was the faculty which separated man and beast, according to Descartes

Jean-Baptiste Bouillaud (1796-1881)

Bouillaud (1825): 100 patients with speech loss after frontal lesions

Brain disease and speechlessness 1761, 1825, 1829-40

• Morgagni, Bouillaud, Andral• N =10, 25, 11

– 5 LHD (4 aphasic); 5 RHD (1 aphasic)– 11 LHD (8 aphasic); 14 RHD (4 aphasic)– 5 LHD (3 aphasic); 6 RHD (0 aphasic)

• Speechlessness rates– 15 of 21 left brain damage (71%)– 5 of 25 right brain damage (20%)

• Meta-analysis (n=46) reveals statistical patterns missed by smaller bins

Swing back to Localization

• Marc Dax (1836): LH damage associated with verbal memory deficits – (Son gave academy

father’s memoirs, 1863)

• Paul Broca (1861 and 1865) convincing evidence of anterior lesions, then speech laterality; Tan “Nous parlons avez l’hemispheregauche”

Paul Broca (1824-1880)

Right Hemisphere as Minor Brain

Carl Wernicke (1874): other left-sided lesions lead to different speech problems

Temporal lesion disturbs comprehension. Developed connectionism model of language and

predicated conduction aphasia

Right brain superiority for some functions

“Leading hemisphere” hypothesis (1868) =

brains are not mere duplicates - RH superiority for visual

recognition

Wilder Penfield, 1930s

• Electrical stimulation lead to language disruption, others produce episodic memories

George Ojemann

• Electrical Stimulation reveals focal representation of language, but differs between individuals

Korbinian Brodmann(1868-1918)

(1906) - 52 cytoarchitectonic brain areas

Last kicks of holism

• Lashley’s Principle of Mass Action– Lesion size, and not location, determine behavioral

consequence • Larger lesions have greater behavioral repercussions

– No clear area-function specifications in rats

• Refuted by Irle (1990) review of 283 monkey studies– Location important– And in fact, some lesions led to improved performance (possibly

due to reciprocal inhibitory networks), with larger size leading to better performance for some functions

EXCEPT Hologram theories of the brain and universe (Bohm, 1980) and Karl Pribram

LECTURE 2Evolution of Handedness

• Nature vs Nuture– Evidence of cultural mechanisms or other

environmental causes– Evidence of genetic basis

• Evidence of right-handedness in early humans

Plato Aristotle (427-347) (384-322)

Aristotle: Right side is the origin of motion in all creatures

Plato favored symmetry

Evidence from early humans

• Evidence from early humans– tools, weapons, cave drawings

• Stone tool manufacture 1.8 mya suggests right-handedness (twist of chips)

• Tooth wear due to toothpicks 1.5 mya indicates right-handedness in Homo habilis

• Preferential wear on cutting tools suggest right handedness• Refitting stone tools (c7000 BC) to the original rock to

indicate clockwise (Rh) manufacture• Early art shows right handedness in sword use• Coren & Porac (1977) surveyed 5000 years of art depicting

unimanual tool or weapon use – 93% Rhanded, and no systematic trends through time (but only 37 pieces prior to 3000 BC)

– Hand outlines – 70% are of the left hand

Rate of Right hand to carry out action in art across eras

8 % Left handed

Biblical evidence

• c1400 B.C. - Judges 20: Of the children of Benjamin, 700 of 26,000 were “restricted in their use of the right hand”– i.e., left-handed = 2.7%

• Psalm 137 connects cunning of right hand and use of tongue (i.e., speech)

If I forget thee, O Jerusalem, let my right hand forget her cunning. Let my tongue cleave to the roof of my mouth…

– However Hebrew writing flows right to left, suggesting left-handedness

– Philologic evidence: both Greek and Latin use same word stem for “ten” and “right” suggesting a left-to-right counting motion

(Task) Hemisphericity & Hemispheric Dominance

• Hemisphere which houses major higher functions (language vs spatial & emotion)\– Handedness informs us of certain task

hemisphericity such as speech

• Dominance: Hemisphere which dominates individual’s cognition (or cognitive style)

Visual Pathway

Elevated Prevalence in:

• Alcoholism• Criminals• Lawyers• Autism• Math prodigies• Gifted children• Immune disorders• People having

paranormal experiences

• Professional tennis & baseball players

• Recent Presidents• Smokers• Sleep difficulties• Stutterers• Vegetarians• Artists

Distribution of Left Handedness

• MZ =14.5%• DZ =14.0%• Single births = 8.5%

Causes of Left Handedness

• NUTURE (environmental)– Prenatal/perinatal brain injury

• 7.3% in normal elementary schools • 18.2 % in special education facilities (in 1920, both)

– Cultural or evolutionary pressure for right handedness

• NATURE– Genetic (e.g., Annett’s 1974 right shift hypothesis)– Mirror twin

Right Shift Hypothesis (Annett, 1974)

• Genetic composition for asymmetry (right or left handedness)

• Single dominant gene for right-shifting RS++ = right handedRS+- = right handedRS-- = half right, half left

• Population made up of:– 70 % right handed, 20 % mixed, 10 % left handed

Right Shift Hypothesis (Annett, 1974)

• Rife (1940) Survey of offspring handedness given parental hand

• R-R: 92.4% (total individuals: 1993)• R-L: 80.5% (174)• L-L: 45.5 % (11)

• Meta-analysis from Ramaley (1913), Chamberlain (1928), and Annett (1973) found 139 LxL family children, 61 left handers (44%)

Twin handedness ratesZazzo, 1960

• MZ (n=1210)– RR: 72 % RL: 24% LL 4%

• DZ (n=1145)– RR: 76 % RL: 22% LL 2%

• Twins(11.7 %) vs singletons (7.1%)(Davis & Annett, 1994)

Simian Handedness:Watanabe & Kawai (1984)

• Wheat Washing: – 6 Rh, 8 Lh

• Potato Washing: – 0 Rh (+6), 1 Lh (+14)

• Mori (1975) reported hand preferences in 5 of these monkeys – all 5 maintained same preference 10 years later

Gorilla Data (Shafer, 1993)Right hand Left hand No Pref

Touch self 18 14 25

Touch Other 6 3 17

Hit 5 1 12

Eat 19 11 17

Small Object 15 5 22

0

5

10

15

20

25

30

Touchself

TouchOther

Hit Eat SmallObject

Right hand

Left hand

No Pref

Gorilla by Age Group vs Human Children (Shaffer, 1993)

0

5

10

15

20

25

30

adult gorilla juvenile children

Right bias

Left bias

no bias

...And Then There Was One • Sixteen Species of Extinct Humans • Ardipithecus ramidus

Australopithecus anamensisAustralopithecus afarensisAustralopithecus bahrelghazaliAustralopithecus aethiopicusParanthropus boiseiParanthropus robustusAustralopithecus africanusAustralopithecus garhiHomo rudolfensisHomo habilisHomo ergasterHomo erectusHomo antecessorHomo heidelbegensisHomo neanderthalensis

• Homo sapiens

Neoteny – Childlike features into adulthood

Wada test

• Used to determine whether psychosurgery (e.g., temporal lobectomy) can be done without risk to memory or speech.

• Anaesthetic (sodium amytal) is injected into artery (via the catheter), paralyzing one hemisphere of the brain for about 3 minutes.

• During this time,memory and speech are tested. The same is then done on other hemisphere.

Unilateral Dysphasics

• WWII British Dysphasics after unilateral damage (Annett, n=224)

• Right handed– Left lesion: 190 (94%)– Right lesion: 13

• Left handed– Left lesion: 14 (67%)– Right lesion: 7

• TBI studies (Zangwill 1967)

• 58/108 Lh/left lesion (54%)• 30/98 Lh/right lesion (31%)

• 657/1147 Rh/left lesion (57%)• 32/990 Rh/right lesion (3%)

• 10% of the population is Left Handed

• Left handers have different brain organization

70%LH

15%RH

15%both

Speech ControlLeft handers

95%LH

5%RH

Speech Control Right handers

What is left-handedness?What is left-handedness?

Handedness and Brain Organization

Gender Differences

• Teen M=13%

• Teen F= 10.5%

Gender differences across the century

Left-Handedness Across the Life Span

• Proportion of left handers drops with age– 14% of 10-year-olds– 4% of 50-year-olds – 2% of 80-year-olds

• Cause is unknown– Longevity hypothesis– Modification

hypothesis (cultural pressure)

Curse or blessing?

• Possible disadvantages of Left handedness– Left-handers are 6x to die in

an accident, and 4x to die while driving

– More likely to have their fingers amputated by power-tools, suffer more wrist fractures (Corliss, 1984)

– Lefties are more susceptible to allergies, reading disabilities, and migraine headaches (Geschwind and Behan, 1984)

• Possible advantages– Lefties are more common among baseball and tennis

players, architects and artists • 21% male math students are Lh vs 11% baseline , 44% non-

Rh vs 24% baseline (Annett & Kilshaw, 1982); 18/59% Lh/nonRh male math professors

• 30% art students were Lh vs 10% controls (Mebert & Michel, 1980)

• Precocious verbal SAT, 24% Lh in males, 12% Lh in females• 18% pro baseball, 17% male top tennis players (Wood, 1988)

– Corpus callosum is 11% greater • Possible greater integration of both brain hemispheres in

processing information

LECTURE 3Phylogeny of Hemispheric Specialization

• Two forms of evolution– Divergent (common ancestor)

• E.g., primate precursors for morphology, speech, etc

– Convergent (common environmental pressures)• E.g., flight appeared independently in insects,

birds, bats, and pterodactyl

• Structure and Function

EVOLUTION OF FUNCTIONAL LATERALITY

Birds• LH lesion of hypoglossal nerve disrupts birdsong:

– no recognizable syllables or discrete phrases.– permanent reduction (RH partially takes over)– full recovery using RH if 1st song season

• RH lesion doesn’t disrupt birdsong:

– normal phrase org., mild reduction of syllables(Nottebohm, 1981)

Not universal to birds: parrots appear to have a bilateral representation of the vocal apparatus.

Non-Mammalian• Chicks categorize grain as separate from inedible pebbles with right

eye (LH) and not with left eye. Also shown in pigeons: pecks faster and consumes more seeds using right eye

• Also in recognition of conspecifics. – Chicks tested using left eye direct more pecks at unfamiliar chicks,

whereas those using right eye did not discriminate between familiar and unfamiliar chicks.

– Mosquito fish prefers to swim with a conspecific on left side while monitoring a predator with right eye.

– Lizard Anolis sp. prefers to direct agonistic responses toward conspecifics on its left side

– Toad Bufo marinus preferentially lodges attack strikes at conspecifics in its left hemifield

General tendency to respond (approach or to attack) to conspecifics on the left side in many species.

Mammalian FUNCTIONAL LATERALITY

Rats & Cats (Structure & function)• Cat, rabbit, rat RH larger &/or heavier• Male rat RH hippocampal & ~cortical thickness• RH intact rats: greater fear response and muricide Toothed whales• Swim counterclockwise in captivity. (greater activity in

opposite hemisphere => RH)• R eye preference to objects, food, people• Echolocation projected slightly left (L ear)• Unihemispheric sleep

Unihemispheric Sleep

Greatest evidence of hemispheric independence

Evolution of Hemispheric Specialization in Apes

Cerebral Torque

Sylvan Fissure Asymmetry

• Left = line, Right = curls

Planum Temporale

100 postmortem brains showed left planum temporale was larger than the right in 65% of cases (Geschwind and Levitsky, 1968).

True 3D measurements reveal no size difference between the left and right planum temporale, previously reports largely an artifact of the methods employed.

Asymmetries reflect differences in gross cortical folding and in the definition of the boundaries of this region (Loftus et al., 1993).

• Old and New World monkeys show SF asymmetry, including chimpanzees, orangutans, rhesus monkeys, common marmosets, and tamarins.

• Found in human fossils and infants, and, interestingly, in the male cat.

Functional Asymmetry in Macaque• In Japanese macaques, a right-ear (LH) advantage

found for discriminating vocalizations of conspecifics. (LH’s role confirmed by lesion studies)

– Species different from macaques did not exhibit asymmetries when tested with macaques calls, suggesting that signals have to convey signification to elicit cerebral lateralization.

• LH of split-brain macaques better at discriminating line orientations, RH for face discrimination. RH advantage for recognizing human facial expressions ("happy" vs. "neutral" face) found for chimps, using chimeric stimuli . Facial expressions of fear and threat in rhesus monkeys were stronger on left side of face.

– Like humans, RH specialized for perceiving & producing emotional behaviors

• THUS hemispheric asymmetries per se is neither specific to humans nor dependent on language.

– i.e., functional asymmetries (e.g., for face recognition) were found in human babies well before language acquisition.

Additional mammalian - Functional differences

• RH dominance in – production of facial expressions in humans and

monkeys– spatial processing in rats, chicks, and other birds– controlling negative emotional expressions and

novelty responding in monkeys, rats, and chickens

• LH dominance in – production and/or perception of species-specific

vocalizations in mice, rats, macaques, passerine birds, and humans

• not clear if due to communicative significance or temporal processing of auditory sequences.

Laterality in “Lower” Vertebrates

• Fish: Escape behavior, eye preference, rotational, courtship behavior

• Amphibians: Pawedness, neural control of vocalizations, escaped responses, sexual behavior

• Reptiles: Aggressive responses