Neuro Exam 4: Split-Brain Studies

Front 1

What is a split-brain operation?

Back 1

-aka cerebral commissurotomy
-surgical transaction of major forebrain commissures (corpus callosum, anterior commissure) as well as hippocampal commissure and massa intermedia
-posterior commissure, other mesencephalic midline structures, and basal forebrain structures are spared
-in humans, operation provides relief in some cases of severe, intractable epilepsy

Front 2

What are the effects of split-brain operations in humans?

Back 2

-To outward appearances, no gross defects in simple, everyday activities
-Speech, language, intelligence, memory, and personality are not obviously affected
-Established bilateral sensory-motor coordinations are preserved (e.g., walking)
-Standard neuro exams reveal no clear abnormalities

Front 3

How is vision affected by split-brain operations?

Back 3

-Pattern information in left visual field projects exclusively to right hemisphere and vice versa
-“Simple” information is available to both hemispheres (probably a midbrain function)
-Object location information may be available to both hemispheres (superior colliculus function) (e.g., can point to light positions in either field with either hand; can correctly judge vertical positions of large objects in both visual fields)

Front 4

How is somesthesis (touch) affected by split brain operations?

Back 4

-stereognostic input to one side only reaches contralateral hemisphere (object felt by left hand only known to right hemisphere and vice versa)
-simple touch, crude localization, pain/temp info available to both hemispheres (likely due to bilateral input to reticular formation)

Front 5

How is audition affected by split brain operations?

Back 5

-sounds to either ear received by both hemispheres since auditory pathways are bilateral

Front 6

How is olfaction affected by split brain operations?

Back 6

-odors presented to one nostril are received only by the ipsilateral cerebral hemisphere

Front 7

How is motor information affected by split brain operations?

Back 7

-fine coordination of the distal musculature of one extremity is controlled more effectively by the contralateral hemisphere
-simple movements of a limb may be controlled from either hemisphere

Front 8

How is language affected by split brain operations?

Back 8

-Left hemisphere is superior at all expressive and receptive language functions
-Right hemisphere language capabilities vary considerably among patients and range from negligible to well-developed

Front 9

How are other lateralized cognitive functions affected by split brain operations?

Back 9

-Left hemisphere superior for mathematical ability
-Right hemisphere superior for visual-spatial abilities

Front 10

What is involved in experimental set-up of split brain studies?

Back 10

-visual presentations must be brief (less than 100 ms) to be confined to one hemisphere (otherwise eye movements may occur)
-tactile inputs must be out of subject’s field of view

Front 11

What happens if a picture of an object is flashed to one visual field of an individual with a split-brain operation?

Back 11

-That object can be selected from a set through touch only by the ipsilateral hand
-This demonstrates the lateralization of visual pattern and tactile shape information
-Both hand/field matches due equally well indicating ability of either hemisphere to recognize, store, and compare pattern information

Front 12

What happens if an object-name is flashed to one visual field of an individual with a split-brain operation?

Back 12

-The object can be selected from a set only by the ipsilateral hand
-successful performance with left-field presentations of words indicates the ability of the right hemisphere to read simple nouns
-if two different words are flashed to the two sides, the subject verbally reports seeing only the word in the right visual field

Front 13

Can a subject give a fluent verbal description of objects felt by the hands?

Back 13

-Only with objects felt by the right hand

Front 14

What happens if an emotion-provoking stimulus is flashed to the left visual field?

Back 14

-The subject may giggle and become embarrassed without being able to say what was seen
-This shows that the right hemisphere has socially appropriate emotional responses
-This shows that emotional states induced in one hemisphere can spread to both hemispheres

Front 15

How do we know the right-hemisphere is better at visual-spatial relationships?

Back 15

-left hand is superior at drawing geometric shapes and pictures of objects
-left hand superior at arranging colored blocks to match a given pictorial design

Front 16

How do we know the right-hemisphere is better at cross-modal pattern and shape perception?

Back 16

-two half-faces are projected, one to each visual field and the subject points to the face seen in the left visual field as the one he saw
-if verbal names must be given to faces or particular features are labeled then the face shown to the right visual field is reported (indicates left hemisphere can recognize a complex visual pattern like a face only when it is analyzed into specific features, not as a whole)
-visual nonsense shapes and simple visual pictures identified more readily in left visual field

Front 17

What language ability is found in the right hemisphere in split brain patients?

Back 17

-language comprehension

Front 18

What logic functions can the right hemisphere do?

Back 18

-appreciate class relationships and similarities (e.g., if picture of cigarette flashed to left visual field, then left hand selects ash tray as most closely related object)
-appreciate logical sequence of acts
-simple arithmetic (add/subtract numbers to left visual field)