B&C: Hemispheric Specialisation

Question 1

Give an example of when lateralisation may not apply to vision?

Answer 1

In certain specific cells such as face specific cells, lateralisation in the brain falls apart a bit

Question 2

Comment on the lateralisation of the motor cortex

Answer 2

Contralateral movement is not absolute, particularly for proximal muscles (shoulders, trunks) movement is largely bilateral

Question 3

What motor control is largely contralateral? Is this always the case?

Answer 3

Only our distal movements (eg fingers.) Although even there, there are some ipsilateral contributions particularly for the non dominant hand

Question 4

Which side are the language area’s usually on the brain, how do they test this (3), and when is this test usually needed

Answer 4

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

Question 5

If a brain does not contain the language areas in the left hemisphere where may they be?

Answer 5

In the right side or processed bilaterally

Question 6

What anatomical differences visible from the outside of the brain could be related to language lateralisation?

Answer 6

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

Question 7

Is there anything to contradict this?

Answer 7

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)

Question 8

Does the difference in grey matter density support this? is this the case for other brain area’s?

Answer 8

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)

Question 9

What differences are there between left and right in regard to cells?

Answer 9

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)

Question 10

What is meant by neural tracers?

Answer 10

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.

Question 11

What differences did these tracers reveal about the left and right hemispheres?

Answer 11

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.

Question 12

What is meant by homotopic and heterotypic areas? Is the brain mostly homotopic or heterotopic

Answer 12

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

Question 13

Other than the corpus callosum, what other brain areas connect the two hemispheres? Give an example of what one of these connect

Answer 13

Anterior commissure and posterior commissure (subcortical nuclei)

Question 14

Give an experimental example of interhemispheric connectivity and how this relates to a practical example

Answer 14

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

Question 15

Why may initial cuts of the corpus collusom not result in major differences in cognition?

Answer 15

May not have cut it fully

Question 16

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?

Answer 16

Says ring but picks up the key

Question 17

Are there any advantages to split brain?

Answer 17

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)

Question 18

What hemispheres appear to be better at what according to these kinds of experiments?

Answer 18

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.

Question 19

When can the left hemisphere match faces just as well as the right?

Answer 19

When verbal descriptions of the face can be made (blonde, brunette etc)

Question 20

What may these advantages be related to?

Answer 20

the right hemisphere more prominently processing ‘the big picture’, doing perceptual organization

Question 21

What evidence is there for right hemisphere processing the big picture? (3)

Answer 21

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

Question 22

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))

Answer 22

Global detection is done faster by RH than LH Local detection is done faster by LH than RH

Question 23

Which hemisphere is more bias to recognising a face as oneself and which has the opposite effect?

Answer 23

Left hemisphere biased towards recognizing self

Question 24

What is meant by the brain interpreter?

Answer 24

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)

Question 25

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?

Answer 25

LH reports seeing it before while RH does not, possibly because it is not concerned with the storytelling

Question 26

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?

Answer 26

LH: matches RH: maximizes

Left hemisphere seeks patterns and sequences in effects

Question 27

How do the two hemispheres differ in structure?

Answer 27

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

Question 28

What difference in brain structure is often seen in kids with dyslexia?

Answer 28

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

Question 29

Was this finding replicated in dyslexic adults?

Answer 29

No, the typical medial temporal lobe asymmetries (left side bigger) were reversed in dyslexic adults