The brain is divided into 4 lobes which can be seen by fissures in the skull. At its highest level the brain is divided in to 2 halves, known as the right and left hemispheres, these hemispheres are designed in an asymmetrical way. This means that each side of the brain is specialized towards specific areas, the right hemisphere dominates visio-spatial tasks and synthetic / holistic thoughts whereas the left hemisphere dominates language especially speech and writing as well as logical and analytical thoughts. These lobes are called; the pre-frontal cortex which primarily deals with higher order thinking, such as personality and processing primary motor and sensory data. The occipital lobe, which deals with visual recognition. The parietal lobe, which deals with recognising sound and linking it to memory, also it deals with a person’s balance and posture through the use of the somatosensory cortex located at the front of the parietal lobe, which is linked with the motor cortex which is located as part of the pre-frontal cortex.. Finally the temporal lobe most commonly known for understanding and producing language which can be traced into two areas, Wernicke’s area, where language is comprehended and Broca’s area, where language is produced.
Language is both localised and lateralised; this can be seen through the use of both split brain patients and normal patients through the use of the Wada test. The Wada test involves temporarily paralyzing one of the hemispheres in the person’s brain; this effectively shuts down that hemispheres language and memory skills so the other hemisphere can be evaluated. Using this method it has been possible to show that while most language skills are innately dominate in the left hemisphere there are some language skills in the right. The reason for this may be that having two language centres within the brain may cause ‘competition’ within the brain which could cause problems such as stuttering. Localisation of language can be seen in Wernicke’s & Broca’s areas, both appear in the left hemisphere, in the temporal lobe, these areas show how localisation works. Wernicke’s area deals with language comprehension while Broca’s area deals with the production of language. Localisation is evident in brain damage patients. Those with damage to Wernicke’s area are unable to comprehend language but can still fluently speak, although because of their lack of comprehension this leads to fluent aphasia. While damage across Broca’s area leads to the patient being unable to communicate but fully able to understand known as non-fluent aphasia.
Furthermore emotion is another major indicator of lateralisation within the brain similar to how language is lateralised, however unlike language the right hemisphere appears to be dominate when it comes to emotion. This was shown in Gainotti (1972) with brain damaged patients. Gainotti looked at patients with brain damage localised to only one hemisphere of the brain, he noticed that those with damage to the left hemisphere showed increased levels of anxiety and aggression while those with right hemisphere damage appeared to show an indifferent or unemotional response. This led him to believe that emotion was focused in the right brain. Further evidence by Etcoff et al (1992) showed their participants people both lying and telling the truth. Etcoff noticed that those with right hemispherical damage were less able to determine who was lying and who was telling the truth while interestingly those with left hemisphere damage were better at detecting the liars than the control who had no brain damage. This lead to the conclusion that the left brain was analytical and would ignore misleading language and pay attention to subtle emotional facial expressions to detect lies. While these studies point to the right hemisphere being dominate in regards to emotion it is possible that each side of the brain is specialised to either positive or negative emotions with the right focusing on negative and the left focusing on positive.
Lobes are not completely independent; they contain sections known as association areas. An association is an area of the cortex scattered around each lobe that helps each lobe communicate with each other. This is done by having, for example, a visual association area in the frontal lobe so that the frontal lobe can determine where objects are located and how far away they are so that when controlling the motor functions it is able to guide your hand to the exact spot it needs to be in to pick up whatever the object is. These motor functions are controlled by another sub section within the brain known as the motor cortex and somatosensory cortex, otherwise known as areas 4 and 6. These two areas are commonly referred to in illustrations of the cortical homunculus which is a pictorial approximation of the motor cortex and shows that areas requiring finer and more precise movement requires more cortical space than those areas which are instinctual responses. The motor cortex can be seen as being arranged contra laterally with the body; this means that the top of the motor cortex deals with the bottom of the body and likewise the bottom of the motor cortex would deal with the top of the body.
Designs of the functional organisation of the brain as shown by the cortical homunculus illustration cannot be seen as entirely accurate. The localisation model of the brain is seen as completely contradicting model which provides purely scientific data as is shown in patients that suffer damage to a lobe, for example a person with damage to the occipital lobe are likely to suffer from visual agnosia or blindness, the localisation model would then therefore say that if an association area was damaged then it is likely that the sense or controlled mechanism would be equally impaired from damage in this area. This contradicts Lashley’s equipotentiality concept as Lashley’s concept would suggest that damage to an association area would not necessarily impair brain function no matter which part of the brain that specialized in vision was damaged, this is because he believed that every part of the brain could do the job of any other brain area because of its elasticity. The problem however with this model is that it was researched on birds using ablation techniques (the removal of pieces of the cortex) whereas localisation research was done on humans. The problem however with localisation research is that it was looked at too narrowly and researchers were not looking at the brain as a whole but more the effect that a single area had on the behaviour of the patient.
The equipotentiality concept and localisation models led to the distributed function model of the brain, which is a compromise between the two models as it shows both; how the brain can adapt and re-organise itself in the event of damage, i.e. if a lobe is damaged the brain can ‘rewire’ itself to try and function. Also how in the event of absolute damage (a sense being completely impaired) the brain can use more of its resources to focus on another area such as the use of touch or hearing. Most importantly this model demonstrates how more than one area of the brain is involved in making a mental mechanism work. At the same time this shows where the dominate control area for that mechanism is unlike the equipotentiality concept which would suggest the entire brain is responsible for the mechanism and the localisation model which would suggest only one point of the brain is responsible. Evidence supporting the distributed function model exists in visual processing, language and memory this is evident through the use of split brain studies and brain scan studies such as Tulving (1989). Tulving found that when his participants used the pre-frontal cortex predominately to try to remember episodic memories where as semantic memory showed high levels of activity towards the back of the cortex. Tulving’s findings were then backed up by Maguire et al. (1997) which found that taxi drivers would have high cortical activities in the hippocampus when remembering a route through London as opposed to remembering information about landmarks which showed low activity in the hippocampus. This shows how information can be localised to a specific cortical area at the same time as being used elsewhere.
The main advantage of the distributed function model is that in the event of brain damage it is possible that complete function loss may not occur as opposed to localisation which would mean that if a lobe was damage function would be entirely lost to that mechanism. This can be shown in the case of Phineas Gage in which a tampering iron was driven completely through his skull massively damaging his pre-frontal cortex, and yet after surviving he continued with a normal life, albeit in a different manner, as it was said that his friends no longer saw him as Gage but as someone else.
The brain can further be described as using a cross over system, this means that right side of the brain controls the left side of the body and vice versa, this as well as the lateralization of the brain can be shown through the use of split brain studies. Sperry (1968) studied severely epileptic patients that could not control their seizures through the use of drugs. In this experiment the corpus callosum (thick band of tissue that links the left and right brain along the central fissure of the brain.) of the patients was severed, this effectively severed the links between the two halves of the brain localizing brain seizures to only one side of the brain, by preventing communication between the halves. This meant that the specialization of each hemisphere could be evaluated. Sperry did this by showing the patient an image in the left spatial field, and then the right, when the same image appeared on the right the patient could not recognise what it was, however the patient could write or describe it entirely. More interestingly if the patient was shown an image on the left he could point to a matching object with his left hand but not his right. These both proves that each side of the brain is specialized to a specific function, the right being of a creative nature and the left of a logical nature.
Finally because of the complexity of the human brain and our lack of understanding, it is impossible to fully determine which area of the brain relates to which mental process, to do this we would need to constantly monitor a living brain in natural scenarios. Currently we can only see functional representations of the brain through use of scans such as PET’s and fMRI’s, this makes it difficult to see how the brain reacts to normal stimuli. Where we can see where the brain reacts to stimuli is through the use of EEG’s which measure brainwaves, however this does not allow us to see precisely where the brain is stimulated. Another method we can use is electrical stimulation of the brain (ESB) which tries to stimulate nervous responses. Although this is a good method it is not the same as a nervous impulse. Overall this makes it almost impossible to map the human brain precisely, while we do have rough models these are broad and we cannot determine whether the brain is further specialized beyond what we can see.