localisation

• Localisation of function is the theory that different areas of the brain are responsible for different behaviours, processes or activities
• The human brain has 2 hemispheres connected by a bundle of fibres which acts as a communication pathway so information can be exchanged
• The human brain is contralateral - the right hemisphere deals with the left-hand side of the body, and the left hemisphere deals with the right-hand side
• In the 19th century, surgeons Broca and Wernicke discovered specific areas of the brain that are associated with particular physical and psychological functions
• Broca’s area is mainly involved in language processing
• Broca identified a small area in the left frontal lobe for speech production
• Damage to Broca’s area causes “Broca Aphasia” which is characterised by slow, laboured speech lacking in fluency. Nouns seem unaffected but prepositions and conjunctions cannot be spoken.
• In the 19th century, a man named Leborgne was hospitalised due to an almost complete loss of speech. His case was presented by a physician Broca, who reported he had discovered the cortical speech centre in the middle part of the patient's left frontal lobe. Following a post mortem on the patient, this area was renamed Broca’s area
• Wernicke identified an area in the left temporal lobe responsible for language comprehension. This is Wernicke's area
• Damage to Wernicke’s area causes “Wernicke’s Aphasia”. Patients would produce nonsensical words as part of the content of their speech and have difficulty finding the word they need
• Phineas Gage was in an explosives accident that caused a tamping iron to hurl through his left cheek, passing behind his left eye, and exited his skull from the top of his head taking most of his frontal lobe with it
• Phineas Gage survived this but many accounts said his personality changed from someone who was calm and reserved to someone who was quick-tempered and rude
• Phineas Gage supports the localisation theory because the only part of the brain affected was the frontal lobe and his personality changed, suggesting the frontal lobe is responsible for regulating mood but this was the only change
• Strength of post-mortems:

  • provides vital evidence of an early understanding of the brain
• Limitations of post-mortems:

  • issue of consent
  • doesn't establish causation
• Lateralisation - when a specific function is only found in one hemisphere e.g language centre is only found in the left hemisphere
• The cortex covering the hemispheres are divided into 4 lobes:

  • the frontal lobe
  • the parietal lobe
  • the occipital lobe
  • the temporal lobe
• In both hemispheres of the frontal lobe is the motor area, which controls voluntary movement in the opposite side of the body.
• Damage to the frontal lobe may cause loss of fine movements.
• The motor cortex is important for complex movements which are controlled by many neurons found in this part of the brain. The more complex the movement, the greater number of neurons.
• In both hemispheres of the parietal lobe is the somatosensory area, which deals with sensory information from the skin
• The more sensitive areas of the body such as the hands and face occupy over half of the somatosensory area
• the somatosensory area is separated from the motor area by a valley called the central sulcus
• The occipital lobe is located at the back of the brain and contains the visual area (cortex). Left eye sends information to the right visual cortex and vice versa. Damage to this area can cause problems with sight
• The temporal lobe is the auditory area which analyses speech based information. Damage to this area may result in hearing loss
• Brain scans from Peterson el al 1988 and Tulving 1994 have been used to show Wernicke’s area is active during listening tasks and Broca’s area during reading tasks
• The use of brain scans is reliable due to the standardised procedures and its objectivity. If these scans were to be conducted on other participants there would be a high degree of replication of results
• Dougherty et al 2002 reported on 44 OCD patients who had undergone a cingulotomy (a neurosurgical procedure that involves lesioning of the cingulate gyrus). At post surgical follow up after 32 weeks, 1/3 met criteria for a successful response to the surgery. The success of procedures like these strongly suggests that symptoms associated with serious mental disorders are localised
• Lashley removed areas of the cortex in rats learning a maze. They found the process of learning required all areas rather than specialised areas. This criticises the theory of brain localisation