B&C: Hemispheric Specialisation Flashcards
Give an example of when lateralisation may not apply to vision?
In certain specific cells such as face specific cells, lateralisation in the brain falls apart a bit
Comment on the lateralisation of the motor cortex
Contralateral movement is not absolute, particularly for proximal muscles (shoulders, trunks) movement is largely bilateral
What motor control is largely contralateral? Is this always the case?
Only our distal movements (eg fingers.) Although even there, there are some ipsilateral contributions particularly for the non dominant hand
Which side are the language area’s usually on the brain, how do they test this (3), and when is this test usually needed
Left side of the brain, this needs to be found before performing brain surgery. The Wada test consists of temporarily anethetizing each hemisphere using amobarbital (or sodium etc). It can be tested if it has kicked in by checking if arm movement on the contralateral side is working. If is in the side with language it produces aphasia (inability to speak or comprehend language) Also, the left hemisphere cannot ‘remember’ what the right hemisphere did after it regains consciousness. The right hemisphere, meanwhile, does remember what it did, but cannot express this verbally, only manually
If a brain does not contain the language areas in the left hemisphere where may they be?
In the right side or processed bilaterally
What anatomical differences visible from the outside of the brain could be related to language lateralisation?
The sylvan fissure was much flatter on the left than to on the right which corresponds to differences in the size of Heschl’s gyrus and the Plan Temporale which corresponds to Wernickes area
Is there anything to contradict this?
Size of left vs right Heschl’s gyrus does not match to language lateralization as measured using Wada test; People with right hemisphere speech dominance (RSG) or bilateral speech (BSG) also have larger left sided Heschl’s gyrus, as do left hemisphere speech dominance people (LSG)
Does the difference in grey matter density support this? is this the case for other brain area’s?
Oo difference in gray matter density (measured with VBM) of planum temporale. But clear difference in gray matter density (VBM) of Broca’s area (speech production)
What differences are there between left and right in regard to cells?
Pyramidal cell bodies are larger on the left than on the right in Heschl’s gyrus
(but not in Angular Gyrus, a region posterior to Wernicke, not involved in language)
What is meant by neural tracers?
Injecting a dye into a brain which is taken up by the neurons which transport this dye to all the regions in which it has connections, these connes=ctions are usually organised in pacthes.
What differences did these tracers reveal about the left and right hemispheres?
In area 22 (similar to Wernicke’s) these patches are equally large in left and right hemisphere, but they are more distant apart in the left than in the right (not the case for auditory cortex) There is also greater high-order dendritic branching than that of their homologs in the right hemisphere, which have more low- order dendritic branching.
What is meant by homotopic and heterotypic areas? Is the brain mostly homotopic or heterotopic
Homotopic- One area on one side being connected by the same area on the other side (mostly through through corpus Callosum)
Heterotopic- where one area connects to somewhere else on the other hemisphere.
Most areas are big fat homos
Other than the corpus callosum, what other brain areas connect the two hemispheres? Give an example of what one of these connect
Anterior commissure and posterior commissure (subcortical nuclei)
Give an experimental example of interhemispheric connectivity and how this relates to a practical example
Synchrony between neurons that respond to the same stimulus that activates cells with receptive fields in both hemifields but not when the connections are severed. Also despite processing each visual area in different sides of the brain we perceive a cohesive whole
Why may initial cuts of the corpus collusom not result in major differences in cognition?
May not have cut it fully
A person with split brain is presented with the word key on the left visual field and ring in his right visual field and is asked to say what he has read and pick it up with his left hand, what should be the result?
Says ring but picks up the key
Are there any advantages to split brain?
Almost like two separate minds: patients are better at drawing two seperate perpendicular shapes with each hand. ( or finding odd one out faster because processing both sides at same time)
What hemispheres appear to be better at what according to these kinds of experiments?
Right hemisphere (left hand) is better at spacial/ geometrical tasks) in the majority of cases, however there has been some contradictory results to this. Right hemisphere is also better at recognising (matching) faces.
When can the left hemisphere match faces just as well as the right?
When verbal descriptions of the face can be made (blonde, brunette etc)
What may these advantages be related to?
the right hemisphere more prominently processing ‘the big picture’, doing perceptual organization
What evidence is there for right hemisphere processing the big picture? (3)
Apperceptive and Integrative Agnosia are problems with perceptual organization, binding features into a coherent percept, and are mainly caused by right hemisphere lesions. Only the right hemisphere can distinguish between ‘fat’ and ‘thin’ shapes when ‘amodal completion’ is required to see the shapes (mind filling in the blanks.) Also the Fusiform face area is more prominent in the right hemisphere
What is the difference between the two hemispheres in the hierarchal letter task (Navon task of smaller letters (local) making out the shape of a different letter (global))
Global detection is done faster by RH than LH Local detection is done faster by LH than RH
Which hemisphere is more bias to recognising a face as oneself and which has the opposite effect?
Left hemisphere biased towards recognizing self
What is meant by the brain interpreter?
Post hoc rationalisations: The left hemisphere is trying to explain the actions performed by the right hemisphere (being instructed to laugh or pick up can, explaining choosing the two images etc)
A string of picture are shown in a sequence, another image is then shown which is somewhat related to the sequence but was not presented before. What conclusion does each hemisphere come to?
LH reports seeing it before while RH does not, possibly because it is not concerned with the storytelling
there is 70% chance of getting red and 30% of getting green. What hemisphere would adopt a matching stategy (3 times green and 7 times red) and what would adopt a maximising strategy (100% red) or would there be a difference? What does this demonstrate?
LH: matches RH: maximizes
Left hemisphere seeks patterns and sequences in effects
How do the two hemispheres differ in structure?
The right protrudes in front, and the left protrudes in back. The right is chubbier (actually has more volume) in the frontal region, and the left is larger pos- teriorly in the occipital region, frequently nudging the right hemisphere off center and bending the longitudinal fissure between the two hemispheres to the right
What difference in brain structure is often seen in kids with dyslexia?
MRI studies reveal that the area of the planum temporale is approximately symmetrical in children with dyslexia—a clue that their language difficulties may stem from the lack of a specialized left hemisphere
Was this finding replicated in dyslexic adults?
No, the typical medial temporal lobe asymmetries (left side bigger) were reversed in dyslexic adults