"Discuss the extent to which brain functions are localised, refer to evidence in your answer.

Localisation of function refers to the idea that certain functions and processes are located in specific areas of the brain. There are six main areas of the brain and all perform different functions. 

• Motor area - controls voluntary movements. It is located in the frontal lobe. 
• Somatosensory area - receives sensory information. It is located in the parietal lobe. 
• Visual area - receives and processes visual information. It is located in the occipital lobe.
• Auditory area - analyses and processes acoustic information. It is located in the temporal lobe.
• Wernicke's area - involved in language comprehension. It is located in the left temporal lobe.
• Broca's area - involved in language production. It is located in the left frontal lobe. 

Localisation of function has been supported by case studies such as that of Phineas Gage. Whilst working on the railway, an iron rod went through his brain. He survived, but experienced a change of personality and emotional issues. This evidenced localisation of function as it was believed that the area damaged was responsible for personality.

A strength of the localisation of function theory is that there are case studies which provide evidence. As previously referred to, Phineas Gage's accident caused his personality to change, but little else (except for vision issues in left eye, but this was due to damage to the eye rather than the brain), and was even able to continue with some farm work. As no other functions were damaged long term, such as speech comprehension and production, and movement, it is good evidence of personality being localised in one area of the brain - and the damage suffered by Gage suggests that personality is controlled in the left frontal lobe. This supports localistion of function, as if this were not the case, Gage would have had no functioning due to his accident. This is important as it supports the theory of localisation of function. However, as this is a case study, there may be some weaknesses. It is hard to generalise the location of each function in the brain based on just one case study, as it only involves one individual in a specific incident. There may be alternative explanations for Gage's change in personality, such as lack of pain management or trauma of the accident. It is important to take this into account when defining localisation of function. 

A weakness of the localisation of function theory is that there are animal studies which disprove it. Lashley removed a certain percentage (between 10 and 50%) of the cortex of a rat which was learning a maze. He found that no area seemed more important in learning, and rather the whole cortex was used. This led to Lashley arguing that higher cognitive functions are not localised, but are distributed in the brain in a more holistic way. This provides evidence against the localisation of function theory as, if it were so, then certain areas of the cortex in rats would be more useful than others in learning. However, this is not a beneficial way of studying localisation of functio, as it uses animal studies. Humans are more complex than rats and so any findings cannot be generalised effectively to the human population. This limits the validity of evidence of holism in the brain. This is important as it means that it should be considered whether evidence is effective or not, depending on its origins. 

A strength of the theory of localisation of function is that there is objective, scientific evidence supporting it. Brain scans, usually fMRI, are useful in showing which areas of the brain are active during certain tasks. Petersen (1988) used brain scanning technology to demonstrate how Wernicke's area is active during listening, and Broca's area is active during reading. This shows localisation of function as if the functions were not local to each area, there would be no difference in the scan between reading and listening. These methods which have come about due to technological developments are beneficial as they are objective measures which show localisation of function. This is important as there is clear scientific evidence supporting the theory. 

A weakness of localisation of function theory is evidence supporting plasticity and functional recovery. Plasticity is the ability of the brain to change functionally as a result of new experience. Functional recovery is similar, and uses plasticity during brain injury or trauma to redistribute functions from damaged areas of the brain to undamaged areas, so the function can still be performed. Evidence supporting functional recovery is the case of Gabby Giffords, who was shot at a point-blank range and managed to recover the use of her left arm and leg, ability to speak and understand short phrases and be able to write. Though this is a case study and should not be generalised to all, the case of Gabby Giffords proves that localisation of function is not fixed, but can be transferred from damaged areas to undamaged ones to allow for healing following a traumatic brain injury, such as a gunshot wound. This is important to take note of, as it goes against the ideas of localisation of function, and suggests that the brain is not as fixed as previously thought.