Localisation of functions in the brain

• holistic theory

  = All the parts of the brain were involved in the processing of thought and action.
• Localisation of functions

  = Theory that different areas of the brain are responsible for specific behaviours, processes or activities.

  • Broca and Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions.
• Cortical specialisation

  = Idea that different parts of the brain perform different tasks and control different parts of the body.

  If a certain area of the brain becomes damaged through illness or injury the function associated with that area will be affected.
• Lobes of the brain

  The cortex is divided into 4 centres:

  -Frontal lobe

  -Parietal lobe

  -Occipital lobe

  -Temporal lobe

  Lobe= part of an organ that is separate from the rest, each lobe is associated with different functions.
• Motor area

  = At the back of frontal lobe

  • Controls voluntary movement in opposite side of the body
  • Damage may result in loss of control over fine movements.
• Somatosensory area

  = At front of both parietal lobes

  • Separated from motor area by a valley called the central sulcus
  • Where sensory information on skin (touch, heat, pressure) is represented.
  • The amount of somatosensory area devoted to a particular body part denotes its sensitivity (face and hands occupy over half)
• Visual area

  = In the occipital lobe at the back of the brain

  • Each eye sends information from right visual field to left visual cortex and from left visual field to right visual cortex.
  • Damage to left hemispheres can produce blindness in part of right visual field of both eyes.
• Auditory area

  = Temporal lobes

  • Analyses speech based information
  • Damage may produce partial hearing loss, comprehended language
  • The more extensive the damage the more extensive the loss.
• Language is restricted to the left side of the brain
• Broca's area

  = Area of frontal lobe in left hemisphere, responsible for speech production

  • Damage to Broca's area causes Broca's aphasia which is characterised by speech that is slow, laborious and lacking in fluency. Have difficulty with preposition and conjunction.
• Wernicke's area

  = Area of temporal lobes in left hemisphere responsible for language comprehension.

  • Wernicke was describing people who had no problem producing language but had problems understanding it.
  • Damage causes wernicke's aphasia, produces nonsense words.
• Phineas Cage

  An explosion hurled a metre-length pole through Cage's left cheek, passing behind is left eye and exiting his skull from the hop of his head taking a portion of his brain (left frontal lobe)

  Cage survived but damage to his brain left a mark on his personality, turning him into someone who is quick tempered and rude.

  suggests the frontal lobe may also be responsible for regulating mood.
• Evaluation- evidence from neurosurgery

  Strength of localisation theory= damage to areas of brain is linked to mental disorders.

  • Neurosurgery is a last resort for treating mental disorders, targeting specific areas of the brain which may be involved.
  • Eg: cingulotomy isolates region implicated in OCD.
  • Dougherty reported on 44 who has OCD and underwent cingulotomy, after 32 weeks 30% had met criteria for successful response and 14% for a partial response.
  • Success of surgeries suggests behaviour associated with mental disorders can be localised.
• Evidence from brain scans

  Supports ideas that many everyday brain functions are localised.

  • Peterson used brain scans to show how Wernicke's area was active during a listening task and Broca's area was active during a reading task.
  • A review of long-term memory studies revealed that semantic and episodic memory reside in different parts of prefrontal cortex- they confirm localised areas for everyday behaviours.
  • Therefore objective methods for measuring brain activity provided evidence that many brain functions are localised.
• Evaluation- counterpoint

  Lashley challenged localisation theory

  • Lashley removed areas of cortex in rats that were learning the route through a maze.
  • No areas proved to be more important than any others in terms of the rats ability to learn a route
  • The process of learning required every part of the cortex rather than confined to a particular area.
  • Suggests higher cognitive processes like learning aren't localised but holistic.
• Language localisation questioned

  Limitation= language may not be localised just to Broca's and Wernicke's areas.

  • Dick and Tremblay found 2% think language is just in Broca's and Wernicke's areas.
  • Advances in brain imaging (fMRI) mean neural processes are studied in more clarity
  • Language function distributed more holistically- language streams have been identified across the cortex, including right hemisphere.
  • Suggests language may be arranged more holistically which contradicts localisation theory.