localisation of brain function

Localisation vs holistic theory: The accepted holistic theory in the 19th century stated that all parts of the brain were involved in thought and action processing. Whereas, Broca and Wernicke put forward localisation of function which meant that certain areas of the brain were involved in certain tasks and areas of the body. If a part of the brain is damaged then the task linked will be affected.

Hemispheres: There is the right and left hemisphere which are two symmetrical halves. When one hemisphere dominates a function this is lateralisation. The left hemisphere causes activity on the right side of the body and vice versa. The cerebral cortex (3mm thick) is the outer layer of the brain. This is what separates us from other animals as this is much more developed in humans the cortext appears grey due to the location of cell bodies 

Lobes and functions: The hemispheres are divided into four lobes 

the parietal lobe  front of both parietal lobes somatosensory area separated from motor area by central sulcus (processes sensory info that you pick up from your skin) 

the temporal lobe Auditory area (analysis of speech-based info) - temporal lobes. Damage can cause hearing loss.

the frontal lobe located in both hemispheres is the motor area (involved in regulating movement) - back of frontal lobes. Damage can cause loss of control over fine movements

occipital lobe.deals with visual infomation sends info from right visual field to left visual cortex and vice versa. Thus, damage to the left hemisphere can cause blindness in the right visual field in both eyes

Language area of the brain: Language restricted to left side of brain(hemisphere). In 1880s Broca's area in left frontal lobe responsible for speech production. Damage = Broca's aphasia slow and influent speech.

Wernicke's identifed patients that had no problem producing language but difficulty understanding it so speech fluent but meaningless identified wernicke's area in the left temporal lobe responsible for language comprehension. Damage = Wernicke's aphasia nonsense words part of the content of their speech 

Brain scan evidence of localisation: Petersen used brain scans which showed that Wernicke's area was active during a listening task and Broca's area was active during a reading tasks which shows that these areas have different functions. Tulving's study found that semantic and eposodic memories are in different parts of the pre-frontonal cortex no sophisticated methods of scanning and measuring activity in the brain                       

Neurosurgical evidence:  surgically removing or destorying parts of the brain developed in 1950s Used today for extreme OCD and depression cases. Dougherty investigated 44 OCD patients who had undergone a cingulotomy which lesions the cingulate gyrus. A follow-up after 32 weeks showed that 1/3 had met the criteria for successful response and 14% for partially successful response. This suggests that symptoms were localised.

Case study evidence: Phineas Gage suffered an accident which took out a large part of his temporal lobe. After this he turned from someone who was calm to quick-tempered which indicates that the frontal lobe is responsible for regulating mood.

Lashley's research: Lashley suggests that higher cognitive functions like learning are not localised by distributed in a holistic way. He removed 10-50% of cortex of rats that were learning a maze. The learning required every part of the cortex rather than  certain parts which suggests that learning is too complex to be localised and it requires the whole brain to be involved.

Plasticity: This is another argument against localisation. When part of the brain is damaged and the function associated with it is lost, other areas of the brain appear to reorganise to recover the lost function. Lashley refers to this as the law of equipotentiality - surviving brain circuits become involved so the same neurological action can be performed. For example, many stroke victims are able to recover abilities that were believed to be lost.

localisation of function functions such as movement, speech and memory are performed in distinct regions of the brain (localised) the opposite view is the brain acts holistically to perform functions

Functionally specialised brain areas- motor, somatosensory, visual and auditory cortices are on both sides of the brain Broca and Wernicke area are only in the on left hemisphere (hemispherically lateralised)

Hemispheric lateralisation- each hemisphere of the brain right (visual-spatial processing) and left (language centers) is specialised to perform different functions language centres are in the left hemisphere visuospatial tasks are best performed by the right

Cortex- surface layer of the brain referred to as grey matter contains mostly cell bodies 2-4mm thick and folded for extra surface area for processing white matter in the brain is mostly myelinated axons

Contralateral- each hemisphere of the brain right and left controls the opposite contralateral side of the body including both motor and sensory pathways and vision and of the contrateral visual field