Localisation in the Brain Flashcards
Localisation of Function in the Brain
Our movements, speech and memory are controlled by different parts in the brain and thus have certain locations within the brain. Before this explanation, the holistic explanation that argued that our function was controlled by all parts or large areas of the brain rather than specific parts were used.
There are 6 parts of the brain that show localisation of function:
6 Parts that show Lateralisation
Cortex - the grey matter and the outer layer of the brain, the mass of cell bodies where much of the brain processing takes place.
The first 4 are found in both parts of the brain. But Broca and Wernicke’s areas are on the left hemisphere.
Hemispheric lateralisation- this is the different sides of the brain, so the left and the right side, are responsible for specific functions. The left controls language and logic whereas the right controls things like visual-spatial tasks.
Visual, motor and somatosensory are contralateral, this means that each hemisphere of the brain eg. the left and the right, control the opposite side of the body, for instance, if the left visual hemisphere is damaged, it will instead affect the right.
VISUAL: function in the cortex
It is in the occipital lobe and at the back of the brain. It deals with visual things, firstly, visual procession would actually start in the retina, at the back of the eyes. Damage to this cortex can cause partial or complete loss of vision, for instance, damage to one cortex can lead to the loss of vision in the opposite visual field as it is contralateral.
MOTOR CORTEX: function in the cortex
At the back of the frontal lobe, carries out voluntary movements in the opposite side of the body, damage can lead to loss of muscle function or even paralysis. But this occurs on the opposite side of the damage because it is contralateral. Different parts of the motor cortex enforce control over different parts of the body and therefore are arranged next to one and another eg. The region that controls the action of the foot is next to the region that controls legs.
SOMATOSENSORY CORTEX: function in the cortex
At the front of the parietal lobe. Receives sense impressions from around the body. It is also contralateral which means damage to one side can lead to loss of sensation, ignoring areas of body, or loss of ability in recognising objects they feel can damage the other side. Both hemispheres have a somatosensory cortex, and it is contralateral.
AUDITORY CORTEX: function in the brain
Top of the temporal lobe and it receives and processes sound information from ears. Damage can lead to deafness.
BROCA’S AREA: function in the cortex
Discovered after the case study of Tan where he could understand everything that was being said to him but only produced the word ‘tan’. In the frontal lobe. Responsible for speech production. Damage to this area, as suggested by Brocas, can lead to Broca’s aphasia where they have hard time producing fluent speech, or have slow speech or speech that has missing words which leads to poor grammar.
WERNICKE’S AREA: function in the cortex
Next to the auditory cortex, so in the temporal lobe. It is responsible for speech comprehension, so being able to understand what is being said. This was discovered after the case of individuals who produced fluent speech but it made little sense. Damage can lead to Wernicke’s aphasia which results in difficulty understanding speech or written language, their speech may sound fluent but it lacks meaning or has nonsense words.
GLOBAL APHASIA: function in the cortex
this is what damage to both Brocas and Wernike’s area can lead to. This is the inability to both produce or understand speech.
- CONTRADICTORY EVIDENCE (EQUIPOTENTIALITY THEORY)
There’s contradicting view through the equipotentiality theory by Lashley who argues that basic motor and sensory functions were localised, but higher mental functions were not, and instead they were distributed in a holistic way. This was supported Lashley’s study with rats where they ran a maze before and after their brain cortex was removed. He found their ability to successfully re-run the maze was affected by how much of the cortex was destroyed, rather than the areas. And because of this, he suggested that the brain has equipotentiality. The more the brain is destroyed the worse their functioning becomes, less the brain is destroyed the less impact it leaves. To support this, other psychologists also argue that because of the high connectivity of the brain, no area is independent and that they all work together. Because of this they argue that the theory of localisation is biologically reductionist because they try to reduce complex processes by claiming that it is done through specific parts of the brain. Thus, they argue that a deeper understanding of the brain is required to truly understand its complex nature. However, a limitation of his work is that there is a problem with extrapolation as the study was conducted on animals, and therefore cannot be generalised to humans as there are many biological differences and have a higher cognitive functioning that may have impacted the outcome of the research, thus making the findings invalid for human research.
- COMMUNICATION IS MORE IMPORTANT
Another limitation is that researchers argue that communication may be more important than localisation. They claim that we need to study the way the brain communicates with each other rather than seeing what regions control what function. Wernicke argues that although different areas are independent, in order to function, they must work together. This is supported by Dejerine who described a case study in which a man could not read because of his broken connection between Wernicke’s area and visual cortex. This therefore shows how interactions between areas produce complex behaviours and damage to the connection between any two points can lead to impairments. This reduces the credibility of localisation as this is not considered.
+ RESEARCH SUPPORT
There is research support from patients who have aphasia to show the existence of language centres. They found that damage to Broca’s area could lead to expressive aphasia which results in the person not being able to produce fluent speech or miss words when speaking. Damage to Wernicke’s area can lead to receptive aphasia where a person cannot understand what is being said to them. Global aphasia is where both Wernicke’s area and Broca’s area are damaged so the person cannot speak or understand. This is a strength as it highlights the importance of the language centres but also has positive economic implications as it allows functioning members to return back to society. Nevertheless, scientists argue that the dominance of their classic model is a consequence to medical practices as there are many researchers who say that there are more regions that produce speech and by not considering this, it shows how we are relying on old and outdated areas which would not have significance in the modern world. Furthermore, emphasis on idiographic methods reduces scientific credibility as it is done on a single person with rare characteristics thus showing how it cannot be used to generalise to the wider target population as everyone’s experience is unique. To move towards a scientific way of doing the study, they could have used a nomothetic approach instead with a larger group.
