localisation of function and lateralisation

localisation vs holistic

  • Paul Broca and Karl Wernicke → discovered different functions of different parts of the brain

  • before this scientists supported the holistic theory of the brain

  • Broca and Wernicke argued for localisation of function → diff parts of the brain have diff functions and are involved with diff parts of the body

hemispheres

  • lateralisation → diff physical/psychological functions are controlled or dominated by a particular hemisphere

  • left side of the body = right hemisphere

  • right side of the body = left hemisphere

  • language = left hemisphere

centres of the brain

  • cortex (outer layer of both hemispheres) is subdivided into 4 sections (lobes) : frontal, parietal, occipital, temporal

  • back of frontal lobe = motor area (controls voluntary movement in other side of the body)

  • front of parietal lobes = somatosensory area (sensory info from the skin is represented - sensitivity) → separated from the motor area by central sulcus

  • occipital lobe = visual area (info from each eye is sent to opposite hemisphere)

  • temporal lobe = auditory area (analyses speech-based info)

language centres (left hemisphere)

  • 1880 → Broca identified Broca’s area (speech production)

  • damage to Broca’s area causes slowed, laborious speech that lacks fluency (e.g. patient that could only say ‘tan’)

  • same time → Wernicke identified Wernicke’s area (could produce language but couldn’t understand it - fluent but meaningless)

  • language is lateralised (only performed by one hemisphere)

functions and lateralisation

  • motor area is cross-wired →RH controls left side and LH controls right side

  • visual is both opposite and same-sided → each eye receives light from left and right visual field (LVF-RH, RVF-LH). allows visual areas to compare diff perspectives and create a full image

split-brain research

  • severing the connections between the two hemispheres to reduce epilepsy (seizures)

  • research show how hemispheres function when they can’t communicate with each other

  • Sperry - studied how two separated hemispheres dealt with different functions (e.g. speech and vision)

  • procedure: 11 people with split-brain studied using images that could be projected to their left and right VF

  • in a normal brain the hemispheres share info to create a full picture, but this can’t be done in split-brain

  • findings: when shown to the RVF they could describe what was seen but couldn’t if shown to the LVF (‘nothing there’) →messages couldn’t be passed between hemispheres so couldn’t apply verbal labels to what’s being seen

  • when they couldn’t give labels they could select a matching object from sight as well as an object most closely associated to the image presented to LVF

  • emotional reaction but reported just seeing a flash of light or nothing when pinup picture shown to LVF

  • conclusion: shows that LH is verbal but RH is ‘silent’ but emotional