AO3 Localisation of function in the brain and hemispheric lateralisation: motor, somatosensory, visual, auditory and language centres; Broca's and Wernicke's areas. Split brain research. Plasticity and functional recovery of the brain after trauma.

There is much evidence to support localisation from brain scans

Petersen used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area was active during a reading task. This suggests these areas have different functions, supporting the notion of localisation of function.

There is also support for localisation of language from aphasia studies

Broca’s aphasia is an impaired ability to produce language, caused by damage to Broca’s area. And Wernicke’s aphasia is an impaired ability to understand language, caused by damage to Wernicke’s area. These findings demonstrate the importance of these brain regions in the production and comprehension of language, supporting the theory that they are localised.

Suggesting higher cognitive functions may not be localised

Not all research agrees with the view that cognitive functions are localised in the brain. Lashley claimed that intact areas of the cortex could take over cognitive functions following injury to the area normally responsible for that function. He investigated rats ability to learn a maze and found basic motor and sensory functions were localised, but higher mental functions weren’t. He found the effects of deliberate damage to the rat’s cortex was determined by the extent, rather than the location of the damage as the more cortex removed, the more the rats ability to learn the maze was affected.

Research into plasticity questions the agrument of localisation

When the brain has become damaged, and a particular function has been compromised or lost, the rest of the brain appears able to recognise itself in an attempt to recover the lost function. Lashley described this as the law of equipotentiality, where brain circuits chip in so the same neurological action can be achieved, although this doesn’t always happen.

Lateralisation changes with age

Lateralisation of function appears not to stay exactly the same throughout an individual’s lifetime, but changes with normal aging. Across many types of tasks and many brain areas, lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults.

individual difference in lateralisation

Brain function lateralisation is evident in the phenomena of right or left handedness, but a person’s preferred hand is not a clear indication of the location of brain function. Although 95% of right handed people have left hemisphere dominance for language, 20% of left handed people have right hemisphere dominance for language function. Additionally, 20% of left handed people have bilateral language functions.

High control over Sperry’s research

Sperry’s brain research used scientific experiments with standardised procedures that were designed to test lateralisation in a highly controlled manner. This meant the findings would have been objective and valid

Contribution of Sperry’s research

Despite there being issues with Sperry’s conclusions, the research has contributed a greater understanding of brain processes and lateralisation.

Issues with generalisation in Sperry’s research

Split brain patients constitute such an unusual sample of people, so only 11 people took part in Sperry’s research, who all had a history of epileptic seizures. It’s been argued that this may have caused unique changed in the brain that may have influenced findings. The control group Sperry used was made up of 11 people with no history of epilepsy so may have been inappropriate to use as the brains of those with epilepsy may work differently to those with epilepsy.

Evidence for plasticity

Kemperman found rats housed in a complex environment showed an increase in neurons in the hippocampus, a part of the brain associated with the formation of new memories and the ability to navigate from one location to another compared to those housed in standard lab cages.

Evidence for plasticity

Maguire studied the brains of London taxi drivers and found significantly more volume of grey matter in the hippocampus than in a matched control group of novice drivers.

Evidence for recovery from trauma

Ballantyne found there is more plasticity for recovery after a stroke in infancy and childhood then in adulthood