last lecture unilateral neglect a representational deficit? a representational deficit? a deficit in...
TRANSCRIPT
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.