Localisation of Function in the Brain Flashcards
What is localisation?
The theory that specific areas of the brain are associated with particular physical and psychological functions
What are the two hemispheres connected by?
The corpus callosum
What is each hemisphere divided into?
The frontal lobe
The parietal lobe
The temporal lobe
The occipital lobe
What is hemispheric lateralisation?
The dominance of one hemisphere of the brain for particular physical and psychological functions. Lateralisation is the fact that the two halves of the brain are functionally different and that each hemisphere has functional specialisations.
What is the primary motor cortex?
Responsible for the generation of voluntary motor movements and is located in the frontal lobe. Motor movements are contralateral meaning the right lobe controls movement on the left side of the body and vice versa. It is somatotopically organised, meaning it is the point for correspondence of an area of the body to a specific point on the CNS. Areas which are finely controlled have larger portions of the cortex whereas coarsely controlled areas have smaller portions.
What is the somatosensory cortex?
The primary somatosensory cortex detects sensory events arising from receptors in the different areas of the body. It is located in the parietal lobe. Using sensory information from the skin, the cortex produces sensations of touch, pressure, pain and temperature, which it then localises to specific body regions. It is contralateral. It is somatotopically organised meaning a specific part of the body is associated with a distinct location in the CNS.
What is the visual cortex?
The primary visual centre is located in the visual cortex. It is located in the occipital lobe. Visual processing actually occurs in the retina where light enters and strikes the photoreceptors. Nerve impulses from the retina are then transmitted to the brain via the optic nerve. It is largely contralateral. It contains several different areas which process different types of information, such as colour, shape or movement. Damage to the cortex can lead to loss of vision but visual perception requires additional input from neighbouring cortical areas and damage to these can lead to loss of specific areas of visual perception, such as prosopagnosia.
What is prosopagnosia?
Loss of ability to recognise familiar faces or identify faces at all.
What is the auditory cortex?
Auditory centre in the brain is concerned with hearing. Most of this area lies in the auditory cortex within the temporal lobes of both hemispheres of the brain. It is contralateral. Auditory areas begin in the cochlea in the inner ear, where sound waves are converted to nerve impulses. These travel to the brain stem where a basic decoding takes place before moving onto the thalamus and then finally the auditory cortex where sound is recognised and interpreted. Damage to the auditory cortex produces difficulties in processing and understanding sounds rather than total deafness.
Is there research to suggest that vision is localised?
Horovitz et al in 1999 found that damage to area VI (a specific area within the visual cortex) leads to a complete loss of all vision including visual images in dreams. When this was damaged, vision was completely lost, suggesting that vision is localised.
Is there research to question the idea of localisation of brain function?
Lashley made lesions into different areas of the brains of rats who were put into a maze. Found large lesions on visual areas impaired maze learning but smaller covering the same brain areas had no effect. Concluded that functions such as learning were spread widely across brain areas. He called this the law of mass action.
Are there case studies to support localisation of brain function?
Phineas Gauge - railroad worker in 1848. He was preparing to blast a section of rock with explosive but accidently hit his tamping iron on the rock causing an explosion to ignite and send a metre length pole through his left cheek, passing behind his left eye and exiting out of his skull, taking most of his pre frontal lobe matter with it. He survived, but the damage to the pre frontal lobe left him with a major change in personality. He turned from calm and polite into bad tempered and rude. The frontal lobe has been linked to regulating mood, which seems to correlate with his change in personality.
Do other factors question localisation of brain function?
Lashley proposed the law of equipotentiality. When the brain is damaged and a particular function is affected, the rest of the brain seems to reorganise itself to recover the lost function (plasticity). Surviving brain circuits chip in so the same neural action can be achieved. This has been shown in documented cases of stroke victims who have recovered abilities originally lost. We should look at the brain in a more holistic way.
Are there case studies that demonstrate localisation of language comprehension and production?
Case study of patient Tan who had damaged his Broca’s area. Broca’s aphasia is the impaired ability to produce language, which is in most cases, caused by damage to the Broca’s area. Wernicke’s aphasia is an impairment of language perception, demonstrating the important role played by this area in the comprehension of language.
Is there contradictory research into the Broca’s and Wernicke’s areas?
Dronkers conducted an MRI scan into two patients with similar brains to Tan to try and confirm Broca’s findings. Although there was a lesion found in Broca’s area, they also found evidence to suggest that other areas may have contributed to the failure of speech production. These results suggest that Broca’s area may not be the only region responsible for speech production and the deficits found in patients with Broca’s aphasia could be the result of damage to neighbouring regions.
