Localisation of function and hemispheric lateralisation

• Somatosensory Cortex:

  • Located in the parietal lobe.
  • Processes sensory information from the skin (e.g., touch, pressure, pain, and temperature).
• Visual Cortex:

  • Located in the occipital lobe.
  • Processes visual information, with each hemisphere receiving input from the opposite visual field.
• Auditory Cortex:

  • Located in the temporal lobe.
  • Processes auditory information, such as sound and speech.
• Broca’s Area: Found in the left frontal lobe; responsible for speech production.
• Wernicke’s Area: Found in the left temporal lobe; responsible for language comprehension.
• Cortical specialisation refers to the idea that different areas of the brain are responsible for specific functions and behaviours. This concept is also referred to as localisation of function.
• Damage to the Broca's area can cause Broca’s aphasia, which results in difficulty speaking but intact comprehension.

  • Studied a patient known as "Tan", who could only say the word "tan" but could understand spoken language.
  • Post-mortem examination revealed damage to a specific area in the left frontal lobe (now called Broca’s area).
• Damage to Wernicke's area can result in Wernicke’s aphasia, where speech is fluent but lacks meaning.

  • Investigated patients who could speak fluently but produced meaningless speech and had difficulty understanding language.
  • Found damage to the left temporal lobe (now called Wernicke’s area).
• Phineas Gage had damage to the frontal lobe which resulted in personality changes, as he became more aggressive, and impulsive and struggled with planning and social interactions.

  • This demonstrated that the frontal lobe controls personality, decision-making and emotional regulation.
• HM has parts of his hippocampus removed, he lost his ability to form new memories.

  • This suggests the hippocampus is critical for memory formation as he could no longer form new long-term memories.
• Outline the difference in function between Broca's area and Wernicke's area (2)

  • Broca’s area is responsible for speech production whereas Wernicke’s area is responsible for language comprehension.
  • Broca’s area enables speech to be fluent whereas Wernicke’s area enables speech to be meaningful.
• A = Broca’s area

  B = Motor cortex

  C = Somatosensory cortex

  D = Visual cortex

  E = Wernicke’s area

  
• A = Somatosensory cortex

  B = Visual cortex

  C = Auditory cortex

  
• Split brain patients show unusual behaviour when tested in experiments. Briefly explain how unusual behaviour in split-brain patients could be tested in an experiment. (2)

  • set up a split visual field
  • images are flashed briefly to one side of the visual field
  • patient asked to verbalise what they saw, only able to do so if image is presented to left visual field.
• The corpus callosum is a large bundle of nerve fibres that connects the two hemispheres of the brain.

  • Its primary function is to enable communication and coordination between the hemispheres, allowing them to work together to process and integrate information.
• In split-brain patients (those who have had their corpus callosum severed), this communication is disrupted, leading to unusual behaviours where the hemispheres act independently.
• The left hemisphere is responsible for speech production (via Broca’s area) and language comprehension (via Wernicke’s area), as well as logical reasoning.
• The right hemisphere is responsible for spatial awareness, emotion recognition and creativity.
• Hemispheric lateralisation refers to the idea that certain mental processes and functions are predominantly controlled by one hemisphere of the brain rather than being equally distributed across both hemispheres.
• Contralateral control refers to the idea that each hemisphere controls the opposite side of the body.

  • The left hemisphere controls the right side of the body.
  • The right hemisphere controls the left side of the body.
• Briefly evaluate research using split-brain patients to investigate hemispheric lateralisation of function (4)

  • the disconnection between the hemispheres was greater in some patients than in others
  • some patients had experienced drug therapy for much longer than others
  • the comparison groups were not considered to be valid as they were often people with no history of epileptic seizures
  • research relates to small sample sizes
• Sperry and Gazzaniga aimed to investigate the extent to which the two hemispheres have specialised functions and how they work independently in split-brain patients.
• Procedure: (visual tasks)

  • patient would fixate on a dot in the centre of the screen
  • images or words were flashed to either the left visual field (processed by the right hemisphere) or the right visual field (processed by the left hemisphere)
  • the patients would respond by selecting/drawing the item with their left or right hand or verbally.
• Procedure: (tactile tasks)

  • Objects were placed in one hand without the patient being able to see them.
  • Each hand’s sensory input is processed by the opposite hemisphere.
  • Patient would identify the item verbally or non-verbally.
• Method: (visual tasks)

  • When words or objects were presented to the right visual field (left hemisphere), patients could describe or name them verbally.
  • When words or objects were presented to the left visual field (right hemisphere), patients could not name them verbally.
  • However, they could draw or select the object using their left hand, showing non-verbal processing abilities.
• Method: (tactile tasks)

  • Objects placed in the right hand (left hemisphere) could be identified verbally.
  • Objects placed in the left hand (right hemisphere) could not be named but could be recognized non-verbally (e.g., pointing).
• Conclusions:

  • Hemispheric Lateralisation: The study demonstrated that the left hemisphere is dominant for language and verbal tasks, while the right hemisphere excels in spatial and non-verbal tasks.
  • Independent Functioning: The severed corpus callosum prevents information transfer between the hemispheres, showing that each hemisphere can function independently in certain tasks.