Last LectureLast LectureLast LectureLast Lecture

Unilateral Neglect Unilateral Neglect a representational a representational

deficit?deficit? a deficit in orienting a deficit in orienting

control?control?

This LectureThis Lecture

History of disconnection History of disconnection syndromessyndromes

The structure of the corpus The structure of the corpus callosumcallosum

The functions of the corpus The functions of the corpus callosumcallosum landmark studies of disconnection deficitslandmark studies of disconnection deficits Independent minds in the same head?Independent minds in the same head? Hemispheric differences revealedHemispheric differences revealed

The Split-Brain SyndromeThe Split-Brain Syndrome

Using hemispheric separation to relieve intractable Using hemispheric separation to relieve intractable epilepsyepilepsy

Sperry, Gazzaniga, Bogen (1962) uncover the Sperry, Gazzaniga, Bogen (1962) uncover the reality of the dual brain, launching a reality of the dual brain, launching a revolution...revolution...

Two minds within a single cranium?Two minds within a single cranium? Differences in hemispheric function.Differences in hemispheric function.

Commissurotomy procedure:Commissurotomy procedure:

Commissures: Projection fibers that connect Commissures: Projection fibers that connect structures on the left & right sides of brain.structures on the left & right sides of brain.

Monkey commissurotomy experiments Monkey commissurotomy experiments in 1930s revealed:in 1930s revealed: little obvious behavioral effects.little obvious behavioral effects. stopped spread of epileptic seizure activity.stopped spread of epileptic seizure activity.

Commissurotomy procedureCommissurotomy procedure

First human operation NY 1940s (Von Wagenen)First human operation NY 1940s (Von Wagenen) Commissurotomy for relief of intractable epilepsy.Commissurotomy for relief of intractable epilepsy. Behavioral testing by Akelaitis revealed Behavioral testing by Akelaitis revealed onlyonly minor minor

motor disturbances.motor disturbances. "... they show clearly that the corpus callosum is "... they show clearly that the corpus callosum is

hardly connected with any psychological function hardly connected with any psychological function at all."at all."

What gets cut?What gets cut?Major interhemispheric Major interhemispheric

Commissures:Commissures: always... always... corpus corpus

callosumcallosum:: connects connects occipital, parietal, occipital, parietal, parts of temporal & parts of temporal & frontal cortices.frontal cortices.

sometimes... sometimes... anterior anterior c.c.:: connects temporal connects temporal and limbic structures.and limbic structures.

sometimes... sometimes... Hippocampal c.Hippocampal c.

never... never... collicular c.collicular c.:: connects superior connects superior colliculicolliculi

Specialization along the Specialization along the Corpus CallosumCorpus CallosumSpecialization along the Specialization along the Corpus CallosumCorpus Callosum

Rostrum- prefrontal cortexRostrum- prefrontal cortex Genu- prefrontal cortexGenu- prefrontal cortex Rostral Body- superior frontal and motor cortexRostral Body- superior frontal and motor cortex Caudal Body-Caudal Body- parietal/somatosensory & temporal/auditoryparietal/somatosensory & temporal/auditory Splenium- visual areas in temporal/parietal and occipital corticesSplenium- visual areas in temporal/parietal and occipital cortices

An MRI of a Split BrainAn MRI of a Split Brain

VIEWS OF VIEWS OF THE CORPUSTHE CORPUSCALLOSUMCALLOSUM

MEDIALMEDIAL

CORONALCORONAL

CorpusCallosumCorpusCallosum

ipsilateralipsilateralheterotopicheterotopichomotopichomotopic

What is connected (via the 200 million + fibers)?What is connected (via the 200 million + fibers)?

1) Homotopic: connect 1) Homotopic: connect homologous areashomologous areas

2) Hetertopic: common 2) Hetertopic: common projection site: ie,projection site: ie,

LV2 --> LV3LV2 --> LV3

RV2 --> LV3RV2 --> LV3 Is it possible so may Is it possible so may

connections could connections could serve NO function???serve NO function???

Before and After...Before and After...

The experimental preparationThe experimental preparation

Myers & Sperry, 1952Myers & Sperry, 1952Myers & Sperry, 1952Myers & Sperry, 1952

Myers and Sperry (1952)Myers and Sperry (1952)

Disconnect Hems. Disconnect Hems. && optic optic chiasm (C)chiasm (C)

Train LH (e.g. circle Train LH (e.g. circle indicates reward)indicates reward)

Test RHTest RH Result: RH has NOT learned Result: RH has NOT learned

the S-R mapping.the S-R mapping. Rule out the chiasm as Rule out the chiasm as

basis for failure (B)basis for failure (B) Conclusion:Conclusion: the corpus the corpus

cal. integrates the cognitive cal. integrates the cognitive operations carried on within operations carried on within each hemisphere.each hemisphere.

intact chiasm &cc cut

Only chiasm cut

A

B

C

Right eye patched

Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962)Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962)

Identified the components Identified the components of the disconnection of the disconnection syndrome.syndrome.

Began to unravel some Began to unravel some mysteries of lateralization.mysteries of lateralization.

Only the LH can Only the LH can name… why?name… why?

Does RH know the LVF Does RH know the LVF stimulus?stimulus?

E: Name what you seeE: Name what you seeS: “fork”S: “fork”

Visual-Verbal DisconnectionVisual-Verbal Disconnection

The RH Knows What it Cannot SpeakThe RH Knows What it Cannot Speak

Response: I didn’t see anythingResponse: I didn’t see anything

View: “Bike” in LVF/RHView: “Bike” in LVF/RH

Left Hand drawsLeft Hand draws the correct responsethe correct response

RH can select what it cannot sayRH can select what it cannot sayRH can select what it cannot sayRH can select what it cannot say

A closer look at disconnectionA closer look at disconnectionA closer look at disconnectionA closer look at disconnection

Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962)Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962)

Components of the disconnection syndromeComponents of the disconnection syndromea) Visual-verbal disconnectiona) Visual-verbal disconnection

b) Tactile-verbal disconnectionb) Tactile-verbal disconnection

c) Visual-visual disconnectionc) Visual-visual disconnection

Impaired matching Impaired matching across the two visual across the two visual fields.fields.

Performance at chancePerformance at chance

E: Same or different?E: Same or different?S: “sameS: “same””

Visual-Visual DisconnectionVisual-Visual Disconnection

Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962)Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962)

Components of the disconnection syndromeComponents of the disconnection syndromea) Visual-verbal disconnectiona) Visual-verbal disconnection

b) Tactile-verbal disconnectionb) Tactile-verbal disconnection

c) Visual-visual disconnectionc) Visual-visual disconnection

d) Tactile-tactile disconnectiond) Tactile-tactile disconnection

e) Motor disconnectione) Motor disconnection primarily contralateral hand control (fine motor movements)primarily contralateral hand control (fine motor movements) Left hand ApraxiaLeft hand Apraxia

Alien Hand SignAlien Hand Sign

Two Minds in One Cranium?Two Minds in One Cranium?

Are 2 consecutive patterns the same or not?Are 2 consecutive patterns the same or not? Compare J.W. with Intact Observers.Compare J.W. with Intact Observers.

Redundant Redundant MixedMixed

TargetTarget

ProbeProbe

J.W. performs better than “normal” in the mixed conditionJ.W. performs better than “normal” in the mixed condition

Holtzman & Gazzaniga, 1985Holtzman & Gazzaniga, 1985

0

10

20

30

40

50

60

70

80

90

Redundant Mixed

ControlsJ.W.

Right Hemisphere Spatial Abilities RevealedRight Hemisphere Spatial Abilities Revealed

PREOPERATIVE

POSTOPERATIVE

RIGHT HANDLEFT HAND

Language Language

LH Dominance:LH Dominance: Note: Language abilities vary greatly among Note: Language abilities vary greatly among

patientspatients Speech production Speech production

single word production by RH in some patientssingle word production by RH in some patients

speech/reading comprehension: speech/reading comprehension: RH vocab ~ age 10 RH vocab ~ age 10

grammar comprehension: grammar comprehension: RH fails at more difficult grammatical constructions.RH fails at more difficult grammatical constructions.

passive voice : The boy was hit by the ball.passive voice : The boy was hit by the ball.

Hemispheric Differences in Matching Letters and LocationsHemispheric Differences in Matching Letters and Locations

Compare verbal vs. spatial matching by LH and RHCompare verbal vs. spatial matching by LH and RH Task: Present target items (letters or location) followed by Task: Present target items (letters or location) followed by

a probea probe Does probe match a target item?Does probe match a target item?

(Reuter-Lorenz & Miller 1998)(Reuter-Lorenz & Miller 1998)

Hemispheric Asymmetries on Basic Visual TasksHemispheric Asymmetries on Basic Visual Tasks

Verbal Spatial

percentcorrect

LH

RH

Corpus Callosum permits access to specialized processingCorpus Callosum permits access to specialized processing

LH dominanceLH dominance Language (comprehension/ production, reading)Language (comprehension/ production, reading) fine motor skills (writing, coordinated fine motor skills (writing, coordinated

movments/gestures)movments/gestures)

RH dominanceRH dominance Visuospatial/constructive abilitiesVisuospatial/constructive abilities

manipulo-spatial tasksmanipulo-spatial tasks

Face processingFace processing Emotion perceptionEmotion perception

Why did previous studies miss these disconnection effects?Why did previous studies miss these disconnection effects?

Sperry’s lab ensured lateralized inputSperry’s lab ensured lateralized input Sperry’s patients had complete callosal Sperry’s patients had complete callosal

section**section** This success inspired study of laterality in This success inspired study of laterality in

the normal brain.the normal brain.