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A* 16 marker on localisation in function
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Essay of 2 pages for the course Biopsychology at AQA (Exemplary essay)
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Discuss localisation of function in the brain (16 marks)Localisation of function refers to the theory that specific areas of the brain are responsible for particular
physical and psychological functions, behaviours and processes. Before investigations such as Phineas Gage,
scientists generally supported the holistic theory of the brain, which is the idea that all parts of the brain were
involved in the processing of thought and action. In contrast, Broca and Wernicke argued for localisation of
function. According to localisation theory, if a certain area of the brain becomes damaged through illness or
injury, the function associated with that area will also be affected.
The cerebrum, the largest part of the brain, is divided into two symmetrical halves called the left and right
hemisphere. Lateralisation is the idea that some of our physical and psychological functions are controlled or
dominated by a particular hemisphere. As a general assumption, activity on the left-hand side of the body is
controlled by the right hemisphere and activity on right-hand side of the body by the left hemisphere.
The cortex of both hemispheres is subdivided into 4 centres, called “lobes”: frontal lobe, parietal lobe, occipital
lobe and temporal lobe. Each lobe is associated with different functions.
The frontal lobe is located at the front of the brain and consists of the motor cortex and Broca’s area. The
motor cortex is positioned at the back of the frontal lobe as is responsible for controlling voluntary movement
in the opposite side of the body. Damage to this area of the brain may result in a loss of control over fine
movements. Broca’s area is responsible for the production of speech.
Behind the frontal lobe is the parietal lobe. At the front both partial lobes is the somatosensory cortex, which
is separated from the motor cortex by a “valley” called the central sulcus. The somatosensory area is where
sensory information from the skin eg touch, heat and pressure, is represented. The amount of somatosensory
area devoted to a particular body part denotes its sensitivity. For example, receptors for our face and hands
occupy over half of the somatosensory area.
The occipital lobe is located at the back of the brain and contains the visual cortex which responsible for seeing
colour and shape. Each eyes sends information from the right visual field to the left visual cortex and from the
left visual field to the right visual cortex. This means that damage to the left hemisphere, can produce
blindness in part of the right visual field area of both eyes.
The temporal lobes contain the auditory cortex and Wernicke’s area. The auditory cortex analyses speech-
based and acoustic information. Damage to this area may produce partial hearing loss. The more extensive the
damage, the more extensive the loss. Damage to the Wernicke’s area, may affect the ability to comprehend
language.
Language is thought to be restricted to the left side of the brain in most people, unlike the areas above which
are found in both hemispheres. Broca, a surgeon, identified the small area in the left frontal lobe responsible
for speech production. Damage to Broca’s area causes Broca’s aphasia which is characterised by speech that is
slow, laborious and lacking in fluency. Broca’s most famous patient was ‘Tan’ – so called because that was the
only word he could say. People with Broca’s aphasia have difficulty with prepositions and conjunctions. Around
the same time as Broca, Wernicke was describing people who had no problem producing language but severe
difficulties understanding it, such that the speech they produced was fluent by meaningless. Wernicke
identified the region now called Wernicke’s in the left temporal lobe as being responsible for language
understanding. This results in Wernicke’s aphasia when damaged. People who have Wernicke’s aphasia will
often productive nonsense words known as neologisms as part of the content of their speech.
One strength of the localisation of function theory is that damage to areas of the brain has been linked to
mental disorders. Neurosurgery is the last resort method for treating some mental disorders, but it targets
specific areas of the brain which may be involved. For example, cingulotomy involves isolating a region called
the cingulate gyrus which has been implicated in OCD. Dougherty et al (2002) reported on 44 people with OCD
who has undergone cingulotomy. At post-surgical follow-up after 32 weeks, about 30% had met the criteria for
a successful response to surgery and 14% for a partial response. This is a strength of the localisation theory as
the success of these procedures suggests that behaviours associated with serious mental disorders may be
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