Localisation of function in the brain Flashcards
what is localisation of function
Localisation of function is the theory that different areas of the brain are responsible for specific behaviours, processes or activities.
localisation vs holistic theory
During the 19th century, Broca and Wernicke discovered specific areas of the brain are associated with particular physical and psychological functions. Before this, 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.
hemispheres of the brain
The cerebrum is divided into two hemispheres. Some of our physical and psychological functions are controlled by a particular hemisphere – this is called lateralisation.
The motor, somatosensory, visual and auditory centres
The cortex of both hemispheres is subdivided into four centres – frontal lobe, parietal lobe, occipital lobe, temporal lobe. Each lobe in the brain is associated with different functions.
motor area
back of both frontal lobes. Controls voluntary movement in the opposite side of the body. Damage to this area can result in a loss of control over fine movements.
somatosensory area
front of both parietal lobes. Where sensory information is processed. The amount of somatosensory area devoted to a particular body part denotes its sensitivity.
visual area
in occipital lobe. Receives and processes visual information. Each eye sends information from the right visual field to the left visual cortex and vice versa.
auditory area
in temporal lobe. Concerned with analysis of speech-based information. Damage may produce partial hearing loss.
The language centres of the brain
Language is restricted to the left hemisphere in most people.
Broca identified a small area in the left frontal lobe responsible for speech production. Damage to Broca’s area causes Broca’s aphasia – speech that is slow, laborious and lacking in fluency.
Wernicke identified a region in the left temporal lobe responsible for language comprehension. Damage to Wernicke’s area causes Wernicke’s aphasia – produce nonsense as part of the content of their speech.
Evaluation of localisation of function (brief)
strength - dougherty et al
strength - evidence from brain scans HOWEVER Lashley
weakness - language may not be localised
strengths of localisation of function
one strength of localisation theory is that damage to areas of the brain has been linked to mental disorders. For example, Dougherty et al (2002) reported on 44 people with OCD who had undergone a cingulotomy – isolating the cingulate gyrus which has been implicated in OCD. At post-surgical follow up after 32 weeks, about 30% had met the criteria for successful response to the surgery. The success of these procedures suggests that behaviours associated with mental disorders may be localised. However, only 1/3 of participants had a successful response to the surgery and the criteria for success was subjective, meaning these results may not be reliable. Therefore this suggests that this study doesn’t fully support the theory of localisation.
another strength is evidence from brain scans that supports the idea that many everyday brain functions are localised. For example, a review of long term memory studies by Buckner and Petersen revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. These studies confirm localised areas for everyday functions. Therefore objective methods for measuring brain activity have provided sound scientific evidence that many brain functions are localised. However, Lashley (1950) challenges the localisation theory. Lashley removed areas of the cortex in rats that were learning a maze route. No area was proven to be more important than any other area in terms of a rat’s ability to learn the route. The process of learning seemed to require every part of the cortex rather than just one particular area. This suggests that learning processes are distributed in a holistic way rather than being localised.
weakness of localisation of function
one limitation is that language may not be localised just to Broca’s and Wernicke’s area. A recent review by Anthony Dick and Pascale Tremblay (2016) found that only 2% of modern researchers think that language in the brain is completely controlled by Broca’s and Wernicke’s area. Advances in brain imaging techniques, such as fMRI, mean neural processes can be studied with more clarity than ever before. It seems that language function is distributed far more holistically in the brain than was first thought. This suggests that, rather than be confined to a couple key areas, language may be organised more holistically in the brain, which contradicts localisation theory.
