Hemispheric Laterlisation and split-brain Research Flashcards
(18 cards)
What is localisation and lateralisation of brain functions?
Localisation is the idea that specific functions of the brain can be generalised to different parts of the brain. However, there are two different sides of the brain; behaviours can be lateralised meaning that one side of the brain controls that function. Some functions are present on both sides of the brain, for example movement and vision.
How is language lateralised in the brain (discuss the left and right hemispheres)
In the case of language, the two main centres are located in the left hemisphere (LH) of the brain. For example, Broca’s area is located in the left frontal lobe and Wernicke’s area is located in the left temporal lobe, meaning language is lateralised to the left hemisphere. The right hemisphere can only produce rudimentary words and phrases but contributes emotional context to what is being said. This has led to the suggestion that the left hemisphere is the analyser and the right hemisphere is the synthesiser.
Which brain functions are not lateralised?
Some functions are not lateralised to one side of the brain, for example movement, hearing and processing information in our visual field.
How is visual processing lateralised?
Processing visual information is more complicated, involving both contralateral and ipsilateral pathways. The left visual field from both eyes is processed by the right hemisphere, and the right visual field from both eyes is processed by the left hemisphere. This enables the visual areas to compare slightly different perspectives from each eye and aids depth perception.
How is auditory information processed in the brain?
Auditory information is processed similarly to visual info, with inputs from both ears processed in both hemispheres. This disparity from the two inputs helps us locate the source of sounds.
What are split-brain operations and why are they performed?
Split-brain operations involve severing the connections between the left and right hemispheres, specifically the corpus callosum. This surgery is a last resort for people with epilepsy, a disorder that causes seizures. During a seizure, excessive electrical activity spreads between hemispheres; cutting the corpus callosum reduces seizures by ‘splitting’ the brain.
Describe sperry’s study
Sperry studied 11 split-brain patients by projecting images to either the left or right visual field. In a normal brain, the corpus callosum shares this information immediately, but in split-brain patients, this communication is blocked.
What happens when an image is shown to the right and left visual field in split-brain patients?
When a picture is shown to the right visual field, participants can describe what they see because the left hemisphere (which controls language) receives the info. But if the object is shown to the left visual field, they usually say there is ‘nothing there’ because the right hemisphere can’t share info with the left hemisphere.
Can split-brain patients identify objects shown to the left visual field?
Yes. While participants could not verbally label objects shown to the left visual field, they could select a matching object with their left hand (controlled by the right hemisphere). For example, when shown a picture of a pinup to the left visual field, they had an emotional reaction but often reported seeing nothing or just a flash of light.
What do split-brain findings suggest about lateralisation?
These findings support the view that the left hemisphere is verbal and the right hemisphere is ‘silent’ but emotional. This shows certain functions are lateralised in the brain.
How does Fink et al.’s PET scan research support lateralisation?
Fink et al. used PET scans with connected brains to show different hemispheres are active during different visual tasks. When attending to global elements (like a forest), the right hemisphere was more active. When focusing on finer detail (like trees), the left hemisphere dominated. This suggests hemispheric lateralisation exists even in connected brains.
What is one strength of split-brain research supporting lateralisation?
Point: Split-brain research shows clear functional differences between hemispheres.
Evidence: Gazzaniga found split-brain participants perform better than controls on tasks like identifying the odd one out.
Explain: This suggests the left and right hemispheres have distinct cognitive strengths, as the left hemisphere’s cognitive strategies are not diluted by the right hemisphere in split-brain patients.
Link: This supports Sperry’s theory of lateralised brain functions by showing behavioural differences when communication between hemispheres is severed.
What is a limitation related to epilepsy in split-brain research?
Point: Epilepsy is a confounding variable in split-brain research.
Evidence: Participants in Sperry’s studies all had epilepsy, but controls did not.
Explain: Any cognitive differences observed may be caused by epilepsy rather than the split corpus callosum alone.
Link: This reduces the validity of conclusions about lateralisation since epilepsy might influence cognitive function independently.
What is a strength of localisation supported by brain imaging studies?
Point: Brain scans provide objective evidence for localisation.
Evidence: Fink et al.’s PET scans showed different brain regions activated for global vs. detailed visual processing.
Explain: This shows the hemispheres specialise in different types of visual information processing even when connected.
Link: Brain imaging strengthens localisation theory by mapping mental processes to specific brain areas.
What is a limitation about the idea of the left hemisphere as analyser and right as synthesiser?
Point: The idea that people have a dominant ‘left’ or ‘right’ brain is misleading.
Evidence: Nielsen et al. analysed brain scans of 1000+ people and found no evidence for dominant hemispheres or personality differences.
Explain: While hemispheric specialisation exists, people do not rely on one hemisphere for all cognitive tasks or traits.
Link: This challenges popular oversimplifications of lateralisation like ‘left-brained’ or ‘right-brained’ personality types.
Describe areas governing movement and where they are found
Areas governing movement are found on both sides of the brain. The motor area is cross wired (contralateral wiring), meaning the left hemisphere controls movement on the right side of the body and vice versa.
What does split brain research tell us about functioning of the brain
Split-brain research shows how the hemispheres function when they cannot communicate.
