Lateralisation And Split-Brain research Flashcards
What is the idea of hemispheric lateralisation?
The two halves of the brainare not exactly alike as although they are structurally identical excluding Broca’s and Wernicke’s area, each hemisphere is lateralised to have functional specialisations e.g neural mechanisms for language are localised primarily in one half of the brain
How come we are able to communicate things in the right hemisphere when language production is located in the left hemisphere?
Our hemispheres are connected via the corpus callosum
How is hemispheric lateralisation studied?
‘Split-brain’ research
How did split-brain research come about?
Surgeons cut the bundle of nerve fibres forming the corpus callosum in an effort to treat severe epilepsy as epileptic seizures are accompanied by intense electrical activity firing across both hemispheres
What is the original study of split-brain research?
Sperry and Gazziniga (1967)
- tested the capabilities of the separated hemispheres
How do visual fields come into play when studying split-brain patients?
. Info from left visual field goes to RH which controls left side of body
. Information from right visual field goes to LH which controls right side of body
As the corpus callosum has been severed, there is no way of hemispheres communicating, so information presented to one hemisphere cannot be received and processed in the other hemisphere.
The fact that Broca’s and Wernicke’s area are only present in the LH has therefore got significant implications
State which hemisphere is lateralised for emotion, language and facial recognition?
Emotion: Right hemisphere
Facial recognition: right hemisphere
Language: left hemisphere
What is the difference between brain lateralisation and localisation?
Localisation refers to how much a specific function occurs in a specific area of the brain, whereas lateralisation focuses on where the function is most dominant, as it has a similar/same function in different areas of the brain but not at the same level
What is hemispheric lateralisation also known as?
Hemispheric asymmetry
What is cerebral dominance?
The hemisphere that does a function the most
What is the difference between localisation and lateralisation?
Localisation focuses on how much one function is located in a specific area of the brain WHEREAS lateralisation assesses the cerebral dominance of any one function
Apart from split-brain research, how is evidence for lateralisation often gathered?
. Wada test
. Dichotic listening tasks
. Divided field tasks
. Brain scanning
How is language lateralised but why is it important not to oversimplify lateralisation?
Language is primarily lateralised in the left hemisphere (cerebral dominance in the LH), but this doesn’t concretely mean that all brain’s are completely specialised for language in the LH. It depends on handedness (whether you are right or left handed)
Why can it be concluded that the majority of individuals have language primarily lateralised in their LH?
95% of right-handed people have it lateralised there, while only 30% of left handed people have it lateralised in their LH. However, the fact that being left handed is a small proportion of the population anyway, the general consensus is that there is cerebral dominance in the LH for language
How is evidence for the lateralisation of language acquired?
The Wada test:
. Anaesthetic is injected into the carotid artery on one side of the head, numbing one hemisphere. When participants had to read aloud, the reading was disrupted in 90% of the people when the LH was anaesthetised
How did Sperry and Gazziniga’s research help to show that the brain is lateralised in the LH for language?
When presented with an image, they could only talk and name the image if using their right visual field as this is controlled by the left hemisphere
Which hemisphere is cerebrally dominant for emotion?
Right hemisphere
What did Gianotti (1972) find about the lateralisation of emotion?
Patients who had damage to their left hemisphere became more anxious and aggressive while patients with damage to right hemisphere became unemotional.
- this shows that emotion is lateralised to the right hemisphere
What was the aim of Sperry and Gazziniga’s original research?
Examine the effects of disconnecting the brain’s two hemispheres on people’s behaviour
What was the method of Sperry and Gazziniga’s research?
. 11 participants
. Patients sat at a table with their hands under a screen or visual stimuli projected onto the screen
. Screen divided left and right halves of visual fields
. Visual stimuli projected for 1/10th of a second
What were the findings of Sperry and Gazziniga’s research?
. The hemispheres have different functions and abilities
- when info was presented to the LVF, the participants couldn’t name what they saw
- if two images flashed at the same time to the right and left visual fields, patients could draw the image they had seen on left half with left hand, but when asked what they’d drawn, they identify what they saw in their RVF.
How did Sperry’s research have good control (scientific)?
. Highly specialised and standard procedures.
. Visual stimuli only projects for 1/10 of a second, not giving enough time for eye movements to interfere with which hemisphere the information goes into
What evidence is there that the differences in functioning between the hemispheres may be overstated (AO3)?
. Kohl and Wishaw (1990) reviewed research into lateralisation and concluded that:
. LH is dominant for processing: letters, verbal memory, arithmetic, all language skills
. RH is dominant for processing: faces, nonverbal memory, spatial abilities and faces
This explains the proposition that it isn’t so much that various functions that are specifically lateralised but that the hemispheres process information differently
- Bradshaw and Sherlock (1982) proposed that the differences between the hemispheres is whether they do analytic vs synthetic (holistic) processing
What are the weaknesses of Sperry and Gazziniga’s research?
. Natural (quasi) experiment, therefore Sperry couldn’t manipulate which groups participants were in
. No controls as you can only have split-brain, can’t compare to ‘normal’ functioning if you have altered your neuronal structure
. Having your corpus callosum severed is rare
. Patients suffered severe epilepsy and were on long term drug treatments, so it may not be valid to compare their brains to ‘normal brains’
Conclusion: limited generalisability
Which research raised the question on whether cerebral dominance can change with age?
Szaflarki et al (2006) - language became more lateralised to the left hemisphere with increasing age up to 25, before lateralisation decreased with each decade of life
