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Functional Localisation and Split Brains - Coggle Diagram
Functional Localisation and Split Brains
Corpus Collosum
(CC)
A massive (
300m axons
) white matter tract that
connects
the two cerebral hemispheres.
Sperry & Myers
Given the size and prominence of the CC, it seemed odd that it would not have an important function.
Given surgeries were going to take place, understanding the function was important.
Found that
CC is important for information transfer
.
Myer's Seminal Experiment
(1956)
Animals were taught to associate on symbol of 4 pairs with a food reward.
They were taught using one eye - this was the
trained eye
, and the other was blindfolded.
Wanted to see what would happen when the animal's used their
untrained
eye.
Interocular Transfer
In a normal animal, if one eye is closed, and a discrimination task is
learnt
- the same discrimination can be recalled using the other eye -
TRANSFER
After CC is cut, the untrained eye acts as if it's never seen the task before -
NO TRANSFER
i.e., the information is
stuck
in one hemisphere
In the normal case, information goes to the visual cortex on
both sides
of the brain.
When information is moved from the
trained eye
to the
untrained eye
, information is already in the brain.
The untrained eye can use the information already in the brain to perform the task
correctly
Interocular Transfer: Cut Chiasm
If the
optic chaism
is cut, the
optic tract
no longer carries information into the
contralateral hemispheres
.
Using the untrained eye, the animal behaves as it did with the trained eye.
Somehow the information transfers to the
untrained hemisphere
Cutting the chaism means that
information cannot cross the midline
The learnt state is stuck in the hemisphere that is trained.
Intermannual Transfer
Glickstein & Sperry (1960)
Normal monkeys and callosum-sectioned monkeys learn tactile discriminations with one hand at about the same rate.
If the
rewarded object and the arm used are swapped
, the normal monkeys show a performance below chance.
Split brain monkeys perform as if the hand has
never seen the task
.
CC
Once the CC is cut, information that is presented to only one hemisphere, it cannot cross into the other.
The animal experiments showed that
commissurotomy
prevented transfer between the hemispheres.