Biopsychology - Localisation of function in the brain and hemispheric lateralisation Flashcards
What is localisation of function?
Belief that specific areas of the brain are associated with specific cognitive processes
Broca’s Area
Function: Responsible for converting thought into speech
Location: Frontal lobe - left hemisphere
Wernicke’s Area
Function: Understanding speech
Location: Temporal lobe - left hemisphere
Aphasia
inability (or impaired ability) to understand or produce speech
occurs when there is damage to either the broca’s or wernicke’s area
Three concentric layers of the brain
The central core
The limbic system
The cerebrum
The central core
Involuntary movements such as breathing/sleeping
Regulates eating and drinking + endocrine system
Homoeostasis: the process by which the body maintains a constant physiological state
The limbic system
Controls emotions
Around the central core
Key roles in memory
The cerebrum
Regulates higher intellectual processes
Contains neuronal cell bodies that are responsible for muscle control and sensory perception
Made up of right and left hemispheres connected by corpus callosum (bundle of fibres) that enable messages exchange between left and right hemispheres
Motor Cortex
Function: Voluntary motor movements
Location: Frontal lobe
Somatosensory Cortex
Function: receiving and processing sensory information
Location: Parietal lobe
Visual Cortex
Function: Processes visual information such as colour shape or movement
Location: Parietal lobe
Auditory Cortex
Function: Concerned with hearing
Location: Temporal lobe
Petersen et al
Petersen et al used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area was active during reading task showing they have different functions
Phineas Gage
Phineas Gage - unique case of neurological damage that supports localisation theory
Gage was involved in an accident where a pole went through the left side of his head damaging his frontal lobe and this affected his personality - went from calm/reserved to quick tempered/rude. This change in personality supports the idea that the frontal lobe is responsible for regulating mood
C: difficult to generalise findings
Case study evidence of
localisation
Plasticity as a criticism of localisation of function
When the brain gets damaged through illness/accident and a particular function is lost, the rest of the brain is able to reorganise itself to recover the loss of function. This suggests that localisation is not fixed to specific areas and the brain is working as a whole unit rather than specific areas for specific functions.
Lashley
Karl Lashley removed (between 10-50% of) area in the cortex of rats placed in a learning maze and found no area was found to be more important than any other in terms of the rats’ ability to learn the maze as learning appeared to require every part of the cortex rather than one area. This suggests learning is too complex to be localised and requires the whole of the brain
Counter evidence of localisation of function
Brain plasticity (Cortical remapping)
refers to the brain’s ability to change and adapt as a result of experience …
Synaptic pruning
frequently used connections are strengthened and rarely used connections are deleted
Research into plasticity
Maguire et al studies the brains of London taxi driver and found significantly more greymatter in the hippocampus than a matched control group
The hippocampus is associated with the development of spatial and navigational skills in humans and other animals
Functional recovery of the brain after trauma
Following physical injury (or a stroke), unaffected areas of the brain are able to adapt and compensate for those areas that are damaged
This functional recovery is another example of neural plasticity
What happens in the brain during recovery?
The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of the damage
Involves:
- Axon sprouting: the growth of new nerve endings which connect with other damaged nerve cells to form new neural pathways
- Reformation of blood vessels
- Recruitment of homologous areas on the opposite side of to perform specific task e.g. of the Broca’s area was damaged on the left, the right side equivalent would carry out its function
Lieperta et a
the brain can only ‘repair’ itself up to a specific point, after which motor therapy or electrical stimulation is needed
Lieperta et al (1998) found that after constraint-induced movement therapy, the motor performance of stroke patients improved significantly.
This shows although the brain has the ability to ‘fix itself’ to a point, this process requires further intervention to be completely successful
limitation of plasticity
Negative plasticity
The brain’s ability to rewire itself can sometimes have maladaptive behavioural consequences. 60-80% of amputees have been known to develop phantom limb syndrome (the continued experience of sensations of the missing limb as it were still there) Ramachandran and Hirsterin found these unpleasant/painful symptoms are due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss
Hubel and Wiesel’
Hubel and Wiesel’s study involved sewing one eye of a kitten shut and analysing the brain’s cortical responses. It was found that the area of the visual cortex associated with the shut eye was not idle (as predicted) but continued to process information from the open eye however human behaviour is very different from animal behaviour, so may not be generalisable to humans
Support from animal studies for plasticity
Kühn et al
Kühn et al recruited 48 people who had not played any computer games for the previous 6 months and randomised them into 2 groups: 23 played Super Mario for at least 30 mins everyday + 25 were just asked not to play any computer games during the study. They found a significant increase in grey matter in various regions of the brain which supports the idea of plasticity and the brain’s ability to adapt as a result of new experience,
Research support for plasticity
Criticism of Maguire’s study
A clear cause and effect relationship between changes in the brain cannot be established as taxi drivers were not tested before becoming taxi drivers so a clear change in the structures of the brain as a result of their experiences cannot be concluded
Hemispheric lateralisation
idea that the two halves of the brain are functionally different and that each hemisphere has functional specialisations,
For example: specialised areas areas associated with language are found in one of the brain;s left hemisphere rather rather than both
What is split-brain research?
A series of studies which began in the 1960s involving epileptic people what had experienced surgical separation of the hemispheres of the brain which allowed researchers to investigate the extent to which brain function is lateralized
Reason for using split brain studies to research hemispheric lateralisation
Communication line between the two hemispheres was removed demonstrated the extent hemispheres were specialised for certain functions and whether the hemispheres performed tasks independently
Procedure of split brain studies
An image would be projected into the individual’s right visual field (processed by the left hemisphere) and vice versa
Findings of split brain studies
When patients were shown a word in their right visual field, they were able to describe what they saw; nevertheless, when they were shown aword in their left visual area, they were unable to describe what they saw.
Conclusion: language functions are exclusively found in the left hemisphere; otherwise, the patient would be able to communicate what they observed in their left visual field (which goes to the right hemisphere)
Strength of the Sperry’s research - methodology
The experiments made use of highly specialised and standardised procedures. Sperry asked participants to stare at a given point - (the fixation point) and the image projected would be flashed for one-tenth of a second so the split brain individual would not have time to move their eye across the images and spread the information across both sides of the visual field and subsequently both sides of the brain. This ensured that only one hemisphere was receiving information
Issues of generalisation with split brain research
There were only 11 people who took part in all variations of the procedure. All had a history eplipetic seizures so it could be argued that this may have caused unique changes in the brain that may have influenced the findings thus the results are not generalisable to wider population
Turk et al
Lateralisation is not fixed…
Turk et al discovered a patient (J.W) who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, eventually leading to the ability to speak about the information presented to either side of the brain. This suggests that language may not be restricted to the left hemisphere and perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.
