Last Lecture Unilateral Neglect a representational deficit? a representational deficit? a deficit in orienting control? a deficit in orienting control?

This Lecture History of disconnection syndromes History of disconnection syndromes The structure of the corpus callosum The structure of the corpus callosum The functions of the corpus callosum The functions of the corpus callosum landmark studies of disconnection deficits landmark studies of disconnection deficits Independent minds in the same head? Independent minds in the same head? Hemispheric differences revealed Hemispheric differences revealed

The Split-Brain Syndrome Using hemispheric separation to relieve intractable epilepsy Sperry, Gazzaniga, Bogen (1962) uncover the reality of the dual brain, launching a revolution... Two minds within a single cranium? Two minds within a single cranium? Differences in hemispheric function. Differences in hemispheric function.

Commissurotomy procedure: Commissures: Projection fibers that connect structures on the left & right sides of brain. Monkey commissurotomy experiments in 1930s revealed: little obvious behavioral effects. little obvious behavioral effects. stopped spread of epileptic seizure activity. stopped spread of epileptic seizure activity.

Commissurotomy procedure First human operation NY 1940s (Von Wagenen) Commissurotomy for relief of intractable epilepsy. Commissurotomy for relief of intractable epilepsy. Behavioral testing by Akelaitis revealed only minor motor disturbances. Behavioral testing by Akelaitis revealed only minor motor disturbances. "... they show clearly that the corpus callosum is hardly connected with any psychological function at all." "... they show clearly that the corpus callosum is hardly connected with any psychological function at all."

What gets cut? Major interhemispheric Commissures: always... corpus callosum: connects occipital, parietal, parts of temporal & frontal cortices. always... corpus callosum: connects occipital, parietal, parts of temporal & frontal cortices. sometimes... anterior c.: connects temporal and limbic structures. sometimes... anterior c.: connects temporal and limbic structures. sometimes... Hippocampal c. sometimes... Hippocampal c. never... collicular c.: connects superior colliculi never... collicular c.: connects superior colliculi

Specialization along the Corpus Callosum Rostrum- prefrontal cortex Rostrum- prefrontal cortex Genu- prefrontal cortex Genu- prefrontal cortex Rostral Body- superior frontal and motor cortex Rostral Body- superior frontal and motor cortex Caudal Body- parietal/somatosensory & temporal/auditory Caudal Body- parietal/somatosensory & temporal/auditory Splenium- visual areas in temporal/parietal and occipital cortices Splenium- visual areas in temporal/parietal and occipital cortices

An MRI of a Split Brain

VIEWS OF THE CORPUS CALLOSUM MEDIAL CORONAL

Corpus Callosum ipsilateral heterotopic homotopic

What is connected (via the 200 million + fibers)? 1) Homotopic: connect homologous areas 2) Hetertopic: common projection site: ie, LV2 --> LV3 RV2 --> LV3 RV2 --> LV3 Is it possible so may connections could serve NO function??? Is it possible so may connections could serve NO function???

Before and After...

The experimental preparation

Myers & Sperry, 1952

Myers and Sperry (1952) Disconnect Hems. & optic chiasm (C) Disconnect Hems. & optic chiasm (C) Train LH (e.g. circle indicates reward) Train LH (e.g. circle indicates reward) Test RH Test RH Result: RH has NOT learned the S-R mapping. Result: RH has NOT learned the S-R mapping. Rule out the chiasm as basis for failure (B) Rule out the chiasm as basis for failure (B) Conclusion: the corpus cal. integrates the cognitive operations carried on within each hemisphere. Conclusion: the corpus cal. integrates the cognitive operations carried on within each hemisphere. intact chiasm & cc cut Only chiasm cut A B C Right eye patched

Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962) Identified the components of the disconnection syndrome. Identified the components of the disconnection syndrome. Began to unravel some mysteries of lateralization. Began to unravel some mysteries of lateralization.

Only the LH can name… why? Only the LH can name… why? Does RH know the LVF stimulus? Does RH know the LVF stimulus? E: Name what you see S: “fork” Visual-Verbal Disconnection

The RH Knows What it Cannot Speak Response: I didn’t see anything View: “Bike” in LVF/RH Left Hand draws the correct response the correct response

RH can select what it cannot say

A closer look at disconnection

Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962) Components of the disconnection syndrome a) Visual-verbal disconnection b) Tactile-verbal disconnection c) Visual-visual disconnection

Impaired matching across the two visual fields. Impaired matching across the two visual fields. Performance at chance Performance at chance E: Same or different? S: “same ” Visual-Visual Disconnection

Human Disconnection Syndrome: Gazzaniga, Bogen & Sperry (1962) Components of the disconnection syndrome a) Visual-verbal disconnection b) Tactile-verbal disconnection c) Visual-visual disconnection d) Tactile-tactile disconnection e) Motor disconnection primarily contralateral hand control (fine motor movements) primarily contralateral hand control (fine motor movements) Left hand Apraxia Left hand Apraxia Alien Hand Sign Alien Hand Sign

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 Mixed TargetProbe

J.W. performs better than “normal” in the mixed condition Holtzman & Gazzaniga, 1985 Holtzman & Gazzaniga, 1985

Right Hemisphere Spatial Abilities Revealed PREOPERATIVE POSTOPERATIVE RIGHT HAND LEFT HAND

Language LH Dominance: Note: Language abilities vary greatly among patients Note: Language abilities vary greatly among patients Speech production Speech production single word production by RH in some patients single 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 Locations Compare verbal vs. spatial matching by LH and RH Compare verbal vs. spatial matching by LH and RH Task: Present target items (letters or location) followed by a probe Task: Present target items (letters or location) followed by a probe Does probe match a target item? Does probe match a target item? (Reuter-Lorenz & Miller 1998)

Hemispheric Asymmetries on Basic Visual Tasks VerbalSpatial percent correct LH RH

Corpus Callosum permits access to specialized processing LH dominance Language (comprehension/ production, reading) Language (comprehension/ production, reading) fine motor skills (writing, coordinated movments/gestures) fine motor skills (writing, coordinated movments/gestures) RH dominance Visuospatial/constructive abilities Visuospatial/constructive abilities manipulo-spatial tasks manipulo-spatial tasks Face processing Face processing Emotion perception Emotion perception

Why did previous studies miss these disconnection effects? Sperry’s lab ensured lateralized input Sperry’s lab ensured lateralized input Sperry’s patients had complete callosal section** Sperry’s patients had complete callosal section** This success inspired study of laterality in the normal brain. This success inspired study of laterality in the normal brain.