Localisation of function in the brain and hemispheric lateralisation:…

The idea

Localisation suggests specific functions reside in specific brain areas, while lateralisation means hemispheres have different roles. The motor cortex (frontal lobe) controls contralateral movement; the somatosensory cortex (parietal lobe) processes touch. The visual centre is occipital, and the auditory centre is temporal. Language is left-lateralised: Broca’s area damage causes non-fluent speech, whereas Wernicke’s area damage produces fluent but meaningless speech. Sperry’s split-brain research showed an image in the left visual field could not be named but could be identified by touch. The brain also shows plasticity and functional recovery after trauma, reorganising through mechanisms like axonal sprouting.

What earns the marks

• Motor cortex in the frontal lobe controlling voluntary movement, with contralateral control stated.
• Somatosensory cortex in the parietal lobe processing sensory information from the skin.
• Visual centre in the occipital lobe and auditory centre in the temporal lobe.
• Broca’s area in the left frontal lobe for speech production, with non-fluent aphasia as the evidence from damage.
• Wernicke’s area in the left temporal lobe for comprehension, with fluent but meaningless speech and neologisms.
• Split brain procedure and method: corpus callosum severed, stimulus presented to one visual field only, so information stays in one hemisphere.
• Plasticity: the brain reorganises with experience, e.g. Maguire et al. (2000) found more grey matter in the posterior hippocampus of London taxi drivers, correlated with time in the job.
• Functional recovery mechanisms named: axonal sprouting, recruitment of homologous areas in the other hemisphere, denervation supersensitivity.
• Evaluation: split brain samples were tiny and had epilepsy, so generalisation is limited; plasticity itself argues against rigid localisation.

Common mistakes and how to put them right

• Swapping Broca’s and Wernicke’s symptoms.

  Put it right: Broca’s damage leaves comprehension largely intact with halting speech; Wernicke’s leaves fluent speech that does not make sense.

• Saying the left hemisphere controls the left side of the body.

  Put it right: Motor and visual processing are contralateral.

• Claiming split brain patients could not see the left visual field image at all.

  Put it right: They processed it, but the right hemisphere has no language to report it.

• Treating plasticity as something only children have, when Maguire’s taxi drivers and studies of adult training show it continues through life.

• Describing functional recovery as damaged neurons growing back, rather than surviving circuits taking over the function.

Exam tips

• Extended response questions require substantial evaluation, so plan two or three well-developed evaluation paragraphs (e.g., discussing plasticity or methodological limits of split-brain research) before writing your description.
• Use case evidence precisely: name the researcher and what was found, because a named finding earns credit that a vague reference to research does not.
• When evaluating localisation, set it against equipotentiality and plasticity rather than simply calling it reductionist.
• In split brain answers, always state which visual field went to which hemisphere before describing the result, or the finding reads as a contradiction.