2. localisation of function Flashcards
During the 19th century, scientists such as Paul Broca and Karl Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions. Before these investigations, scientists generally supported the
holistic theory of the brain - 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: the idea that
different parts of the brain perform different tasks and are involved with different parts of the body. If a certain area of the brain becomes damaged through illness or injury, the function associated with that area will also be affected.
The cerebral cortex is the outer layer of both hemispheres. The cortex of both hemispheres is subdivided into four centres - called the ‘lobes’ of the brain:
the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe.
A lobe is a part of an organ that is separate in some way from the rest - each lobe in the brain is associated with different functions.
The main part of the brain (the cerebrum) is divided into two symmetrical halves called the left and right hemisphere.
As a general rule, activity on the left-hand side of the body is controlled by
the right hemisphere and activity on the right-hand side of the body by the left hemisphere.
Language is linked to the left hemisphere.
The parietal lobe is on the top back of the brain and deals with
orientation and recognition
The frontal lobe is on the front of the brain and deals with
reasoning, planning, decision making and emotions.
At the back of the frontal lobe (in both hemispheres) is the MOTOR AREA which controls
damage leads to
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.
In the OCCIPITAL LOBE at the back of the brain is the visual area (or visual cortex).
Each eye 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, for example, can produce blindness in part of the right visual field of both eves.
At the front of both parietal lobes is the somatosensory area, where
sensory information from the skin (e.g. related to touch, heat, pressure, etc.) is represented. The amount of somatosensory area devoted to a particular body part denotes its sensitivity, for instance, receptors for our face and hands occupy over half of the somatosensory area.
Finally, the TEMPORAL LOBES house the auditory area, which analyses speech-based information. Damage may
produce partial hearing loss. The more extensive the damage, the more extensive the loss.
language is restricted to the
left side of the brain in most people.
In the 1880s, Paul Broca, a surgeon, identified a small area in the left frontal lobe responsible for
speech production.
damage to BROCA’S AREA causes
example - Tan
Broca’s aphasia which is characterised by speech that is slow and lacking in fluency. Broca’s most famous patient was ‘Tan’ - so-called because that was the only word he could say.
Around the same time as Broca, Karl Wernicke was describing people who had no problem producing language but severe difficulties understanding it, such that the speech they produced was fluent but meaningless. Wernicke identified a region (Wernicke’s area) in the
responsible for
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 produce nonsense words as part of the content of their speech.
AO3: strength of LOF
EVIDENCE FROM NEUROSURGERY - Dougherty (OCD)
One strength of localisation theory is that damage to areas of the brain has been linked to mental disorders.
Neurosurgery is a last resort method for treating some mental disorders, targeting 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. reported on 44 people with OCD who had undergone a cingulotomy.
At post-surgical follow-up after 32 weeks, about 30% had met the criteria for successful response to the surgery and 14% for partial response.
The success of these procedures suggests that behaviours associated with serious mental disorders may be localised.
