Lecture 11 and 12: Corpus Callosum and Split-brain Flashcards
What is the Corpus Callosum?
- Large white matter tract with over 200 million axons
- Function
- transfer and integration of information between the two hemispheres
- Interhemispheric communication
What are the other commisural fibres?
- Corpus callosum
- Anterior commissure
- Posterior commissure
- Hippocampal commissure
Here is an image of an structural MRI of the CC
Here is a diffusion MRI (dMRI) of the CC
How did researchers decided how to divide the Corpus Callosum?
- From experiments in monkeys and clinical work in humans
- The regions may be roughly associated with various cortical regions, although there is a considerable overlap
- no exact one-to-one correspondence
True or False
There is not really landmarks on the CC
True,
to divide the CC they really went with measurements and divided it according to portions of the CC
What is the Witelson parcellation?
It’s how the CC is divided
Name the division of the CC
- Rostrum
- Genu
- Rostral Body
- Anterior Mid-body
- Posterior Mid-body
- Isthmus
- Splenium
True or False
You can parcellate the CC as you want
True, there is not rule for how it is divided. You can divide it into 25 subregions as well for example:
True or False
The Microstructure of the CC, is the same across every division.
False.
- The microstructural organization of axons vary along the CC
- Fibre density
- axon diameter
True or False
It is impossible to measure how fast the information is transferred from one hemisphere to the other
False, it can be measured with the Poffenberger paradigm
What is the Poffenberger paradigm?
- 1912
- Measures the interhemispheric transfer time (IHTT)
- Procedure:
- Flash a figure on the left or right visual field and ask the patient to press a button with the left or right hand.
- Measure the time it takes to click the button and subtract the amount of time it takes for the uncrossed reaction (crossed uncrossed difference)
- amount of time it takes to cross the hemisphere
- Results:
- Takes longer when interhemispheric transfer of information is necessary
- Difference is subtle
- Takes longer when interhemispheric transfer of information is necessary
Where does the interhemispheric transfer occur in the Poffenberger paradigm?
- One way of studying this:
- manipulate the motor and visual aspects
- See which manipulation affects more the transfer time
- Another way is to study lesions and see if it take more time or not
What is the Horse Race Model?
- The model says that the transfer probably occurs at both locations at the same time but the motor transfer wins the race because the axons in CC are larger and more myelinated.
- transfers better
You are using the Poffenberger paradigm, what happens if you flash the stimuli in the left visual field and ask the patient to answer with their left hand?
The information stays within the right hemisphere. It doesn’t crosses the CC
You are using the Poffenberger Paradigm and you flash the stimuli in the left visual field and ask the patient to answer with their right hand. According to the Horse Race Model, what happens?
Because the information has to cross to the left hemisphere to move the right hand, both the motor system and visual system transmit the information. According to the Horse race model, the motor transfer is faster and arrives at the left hemisphere first since the axons in the CC are bigger and more myelinated.
True or False
The two hemispheres work together
True.
- Motor coordination
- Language
- affective prosody (intonation in language)
- Emotion processing
True or False
The CC is different depending on the sex of a person.
True,
Some CC subregions are larger in women
True or False
The CC is smaller in left handed people.
False
The CC is larger for left-handed people
What are some acquired abnormalities of the corpus callosum?
- Callosotomies
- Traumatic brain injuries
- Stroke
What are some developmental abnormalities of the corpus callosum?
- Corpus callosum Agenesis
- Variation in developmental disorders
- Autism
Who studied the Split-brain?
- Geschwind
- Sperry
- Bogen
- Gazzaniga
What has Sperry’s role when studying the split-brain?
- He studied the specialization of each hemisphere
- He performed surgery cut of the CC
- initially he didn’t notice any cognitive damage
- After creating the correct tests, he could find specific deficits
- Thus learn about the specialization of the hemispheres
What experiments with Sperry do?
- Mainly with cats and monkeys (with and without cut CC)
- Cut optic chiasm as well
- Procedure:
- Trained the animals to do some task while covering one of the eyes.
- Test
- Tested the training while covering the other eye
- Results:
- Both hemispheres act independently
- What the animals with split-brain learned was not remembered by the other hemisphere. They had to learn it all over again.
- Control group: training transferred to the other hemisphere
When does the split-brain phenomenon occurs?
- when both the CC and anterior commissure (AC) are cut
What experiments were done with humans?
- Participants:
- People with plit CC
- Procedure:
- Visual stimulation
- fixed gaze on the central poin
- lights flashed on both the right and left hemifield
- Tactile stimulation
- Placed object on the right hand
- Placed object on left hand
- Motor control of the hand
- Dictate to the left hemisphere some control over left hand
- Dictate contradictory information to each hemisphere
- Visual stimulation
- Results:
- Visual
- R hemifield → Could say where they saw the light
- L hemifield → Couldn’t say but could point
- Tactile:
- R hand → could name the object
- L hand → not able to name or describe it, but could match it with same object in collection
- Motor
- Poor control (since not the left hemisphere responsible for moving the left hand)
- R hand moved differently from the left
- Visual