Localisation of the brain

• Localisation is the idea that certain parts of the brain are responsible for certain functions.
• Motor, somatosensory, visual and auditory cortex are on both hemispheres of the brain. The Broca's and Wernicke's area are only on the left hemisphere (hemispherically lateralised).
• Left hemisphere specialises in the language centres.
• Right hemisphere specialises in the visual processing of spatial information.
• The brain as a whole can be described as contralateral. This is due to the right hemisphere controlling the left side of the body, while the left hemisphere controls the right side of the body.
• The cerebral cortex is the surface later of the brain and can be referred to as grey matter. It contains mostly cell bodies and are 2-4mm thick. They are also folded for increased surface area.
• White matter in the brain is mostly composed of myelinated axons.
• Occipital lobe is the visual processing centre, where each hemisphere receives information from the contralateral visual field.

  Damage to this area could result in partial or complete loss of vision (known as cortical blindness). Damage to one cortex can lead to loss of vision in the opposite visual field.
• The motor and somatosensory cortex are divided by a fold known as the corpus callosum.
• The frontal lobe contains the motor cortex which is responsible for voluntary movements.

  Damage to the motor cortex may result in loss of muscle function, or after severe trauma, paralysis. This occurs on the opposite side of the body to damage due to contralaterality.
• Parietal lobe contains the somatosensory cortex which is responsible for receiving sensory information from the skin to produce senses related to pain / pressure.

  Damage to this area may result in loss of sensation, ignoring areas of the body (neglect syndrome) and the loss of ability to recognise objects by their feel (agnosia). The effects are in opposite side to damage.
• Temporal lobe contains the auditory cortex and receives auditory information from the environment.

  Damage to this area can lead to cortical deafness, which is where the patient is unable to hear but there is no damage to the structure of the ear.
• Broca's area is located in the left pre-frontal cortex and is responsible for speech production. Damage to this area leads to Broca's aphasia which is difficulty in producing fluent speech and speech is slow.
• Wernicke's area is located in the posterior temporal lobe and is responsible for the comprehension of language. Damage to this area results in receptive aphasia, where an individual has trouble understanding written or spoken language.
• Global aphasia is damage to both Broca's and Wernicke's area, which results in the inability to understand and produce speech.
• Strengths of localisation of function:

  • Supporting evidence - Petersen (1988) used brain scans to scan brains of participants during a listening and reading task and found the Wernicke's area was active in the listening, whereas the Broca's area was active during the reading. This supports localisation.
• Strengths of localisation of function:

  • Neurosurgery evidence - Dougherty et al (2002) studied 44 OCD patients who had the cingulate gyrus removed from their brain removed. Findings showed after 32 weeks, 30% of patients had significantly improved while 14% showed partial improvement. This suggests behaviours associated with serious mental disorders may be localised.
• Strengths of localisation of function:

  • Case study evidence - Phineas Gage (1848) was caught in an explosion where a 1m pole pierced his skull and tore out majority of his frontal lobe. After surviving, he became aggressive, short tempered and rude. This suggests the frontal lobe may be responsible in the regulation of mood (supporting localisation).
• Limitations of localisation of the brain:

  • Case study - Usually viewed as unscientific in brain research with damage covering multiple regions of the brain (as seen with modern MRI of Tans brain).
• Limitations of localisation of the brain:

  • Counter research - Lashley (1925) conducted a study with 50 rats who ran a maze before and after areas of the brain were destroyed. He found the ability to successfully rerun the maze was affected by how much of the cortex was destroyed, not which areas. This suggests that higher cognitive processes such as learning and memory are not localised, but rather distributed across the brain.