LOCALISATION OF BRAIN FUNCTION

→ Refers to the principle that specific functions have specific locations within the brain

→ Many functions have been localised to different areas of the cerebral cortex

→ The cerebral cortex is the outer layer of the cerebrum. It is about 3mm thick and is referred to as ‘grey matter’

~MOTOR CORTEX~

  • Found in both hemispheres of the frontal lobe in a region called the pre-central gyrus

  • Responsible for the generation of voluntary motor movements

  • The motor cortex on one side of the brain controls the muscles on the opposite side of the body

  • Different parts of the motor cortex control different regions of the body

~SOMATOSENSORY CORTEX~

  • Found in both hemispheres of the parietal lobe in a region called the post-central gyrus

  • Detects sensory events arising from different regions of the body, and produces sensations of touch, pressure, pain and temperature which it localises to specific body regions

  • The somatosensory cortex on one side of the brain receives information from the opposite side of the body

  • Different parts of the somatosensory cortex control different regions of the body

~VISUAL CORTEX~

  • Found in both hemispheres of the occipital lobe

  • Responsible for visual processing

  • The visual cortex in the right hemisphere receives its input from the left visual field (LVF) et vice versa

  • The visual pathway begins in the retina, where light enters and strikes photoreceptor cells which convert light into nerve impulses

  • Nerve impulses are then transmitted to the visual cortex via the optic nerve

~AUDITORY CORTEX~

  • Found in both hemispheres of the temporal lobe

  • Responsible for auditory processing

  • The auditory pathway begins in the cochlea in the inner ear where sound waves are converted into nerve impulses

  • Nerve impulses travel via the auditory nerve to the auditory cortex

EVALUATION

Research Support:

→ PRESENCE OF SUPPORTING RESEARCH FROM CASE STUDIES

  • One strength is that there is evidence from case-studies of brain-damaged individuals to support the different functions of Broca’s and Wernicke’s areas in language production and understanding.

  • It has been found that individuals with damage to Broca’s area develop expressive aphasia, which is characterised by speech that is slow and lacking in fluency.

  • Individuals with damage to Wernicke’s area develop receptive aphasia, which is characterised by an inability to extract meaning from spoken or written words.

  • This demonstrates the important role that Broca’s area plays in the production of language and the important role that Wernicke’s area plays in the understanding of language.

→ PRESENCE OF SUPPORTING EVIDENCE FROM BRAIN SCANS

  • Another strength is that there is evidence to support the different functions of Broca’s and Wernicke’s areas from brain scan studies.

  • For example, Peterson et al (1988) used brain scans to demonstrate that Broca’s area was active during a reading aloud task and Wernicke’s area was active during a listening task.

  • This supports the suggestion that these areas of the brain have different functions, providing both concepts with high internal validity.

Conflicting Evidence:

→ MORE COMPLEX THAN PREVIOUSLY SUGGESTED

  • One weakness is that there is evidence that language production is not confined to Broca’s area alone.

  • Dronkers et al (2007)re-examined the preserved brains of two of Broca’s patients. The purpose of the study was to identify the extent of any lesions in more detail by using modern high-resolution MRI imaging.

  • The findings revealed that other areas besides Broca’s area were damaged and therefore could have contributed to the patients reduced speech abilities.

  • This study suggests that language is far more complicated than once thought, and involves networks of brain regions rather than being localised to specific areas.

→ CONFLICTING EVIDENCE

  • One weakness is that there is evidence that certain functions cannot be localised to specific areas of the brain.

  • For example, Lashley (1950) removed areas of the cortex in rats that were learning their way around a maze.

  • He found that no area was more important than any other in terms of the rats ability to learn their way through the maze. The process of learning appeared to require every part of the cortex rather than being confined to a particular area.

  • This suggests that learning is too complex to be localised and requires the involvement of the whole brain.