Localisation of function in the brain

• Firstly, localisation is a theory that different areas of the brain are responsible for different behaviours, processes or activities
• The holistic view took on an approach that all parts of the brain were involved in the processing of thought and action
• Broca and Wernicke argued for localisation of function (also known as cortial specialisation), this is the idea that different parts of the brain perform different tasks and are involved with different parts of the body

• Brain is divided into 2 symmetrical halves called the left and right hemisphere
• Some physical and psychological functions are controlled/dominated by a particular hemisphere - this is known as laterisation
• Activity on the left-hand side of the body is controlled by the right hemisphere
• Activity on the right-hand side of the body is controlled by the left hemisphere 
• Outer layer of the hemispheres is called cerebral cortex which is also known as cortex
• This covers/protects in the inner parts of the brain
• The cerebral cortex is what seperates us from animals because the human cortex is much more developed
• The cortex appears grey due to the location of cell bodies

• Both hemispheres are sub-divided into 4 lobes:
  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
• Each lobes is associated with different functions:
  • At the back of the frontal lobe is an area called the motor area which controls voluntary movement in the opposite side of the body ---- damage to this area may result in a loss of control over fine movements
  • At the front on the parietal lobe is the somatosensory area which is seperated from the motor area by a valley called the central sulcus. Somatosensory area is where sensory information is processed. such as touch
  • The occipital lobe is the visual area, where each eye sends information from the right visual field to the left visual cortex - vice versa. ---- damage to one side of the hemisphere, for example the left hemisphere can cause blindness in the part of the right visual fields of both eyes
  • The temporal lobes is the auditory area, which analyses speech-based information...

---- damage to this area may produce partial hearing loss

• Paul Broca identified a small area in the left frontal lobe responsible for speech production
• Damage to Broca's area causes Broca's aphasia, this is when speech is slow, laborious and lacking in fluency
• Karl Wernicke identified a region in the left temporal lobe as being responsible for language comprehension
• Damage to Wernicke's area will result in Wernicke's aphasia, this is when patients often produces nonsense words as part of the content of their speech. Also, damage to this may result in patients being able to produce language but have severe difficulties understanding it

Brain scan evidence of localisation

• 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 a reading task, suggesting that these areas have different functions 
• Tulving et al, did a study on long-term memory. He found that semantic and episodic memories reside in different parts of the prefrontal cortex. 

Neurosurgical evidence

• Dougherty et al, reported on 44 OCD patients who has undergone a cingulotomy - a neurosurgical procedure that involves lesioning of the cingulate gyrus. 
• At post-surgical follow up after 32 weeks, a third met the criteria for successful response to the surgery and 14% for partial response.
• The success of procedures like this strongly suggests that symptoms and behaviours are associated with serious mental disorders are localised.

Case study evidence

• Phineas Gage 
• An explosion at his workplace caused a metre-length pole to go through Gage's left cheek, passing behind his left eye, and exiting his skull from the top of his head taking a protion of his brain with it - most of his frontal lobe.
• Gage survived the accident, but the damage to his brain had left a mark on his personality - he had turned from someone who was calm and reserved to someone who was quick-tempered and rude. 
• This case study supports localisation because the part of the brain which was damaged was in the prefrontal cortex, this is because the part of the brain damaged in the accident was the area in the frontal cortex associated with planning, reasoning and control. The frontal cortex is important for functions such as reasoning, language and social cognition. This may explain why Gage's personality changed.
• Gage's extraordinary story served as one of the first sources of evidence that the frontal lobe was involved in personality.

Lashley's research

• Karl Lashley's research suggests that higher cognitive functions, such as the processes involved in learning, are not localised but distributed in a more holistic way in the brain. 
• Lashley removed areas of the cortex in rats that were learning a maze. 
• No area was proven to be more important than any other area in terms of the rats' ability to learn the maze. 
• The process of learning appeared to require every part of the cortex, rather than being confined to one area. 
• This suggests that learning is too complex to be localised and requires the involvement of the whole of the brain. 

Plasticity

• An arguement against localisation of function is cortical remapping or plasticity 
• When an area of the brain is damaged, and a particular function has been lost, the rest of the brain appears to be able to reorganise itself in an attempt to recover the lost function.
• Lashley described this as the law of equipotentiality whereby surviving brain circuits 'chip in' so the same neurological action can be achieved.