localisation, hemispheric lateralisation

• localisation of function

  the idea that certain functions like language and memory have certain locations within the brain, meaning that the different areas of the brain are responsible for different behaviours, processes or activities.
• what are the 6 areas (cortex's) of the brain?

  1. auditory area
  2. broca's area
  3. motor area
  4. somatosensory area
  5. visual area
  6. wernicke's area
• what are the 4 brain lobes?

  1. frontal lobe
  2. parietal lobe
  3. temporal lobe
  4. occipital lobe

  
• where is the motor area located and what is its function?

  • located in the frontal lobe.
  • responsible for voluntary movements by sending signals to the muscles in the body.
• where is the somatosensory area located and what is its function?

  • located in the parietal lobe.
  • receives incoming sensory information from the skin to produce sensations related to pressure, pain etc..
• where is the visual area located and what is its function?

  • located in the occipital lobe.
  • receives and processes visual information.
  • information from the right visual field is processed in the left hemisphere, and information from the left visual field is processed in the right hemisphere.
  • contains different parts that process different types of information, including colour, shape or movement.
• where is the auditory area located and what is its function?

  • located in the temporal lobe.
  • responsible for analysing and processing acoustic information.
  • contains different parts, and the primary auditory area is involved in processing simple features of sound, including loudness, tempo and pitch.
• where is broca's area located and what is its function?

  • located in the left frontal lobe.
  • responsible for speech production.
  • damage to this area leads to a speech disorder called Broca's aphasia, where speech can be understood but cannot be expressed coherently.
• where is wernicke's area located and what is its function?

  • located in the left temporal lobe.
  • responsible for speech comprehension.
  • damage to wernicke's area causes a speech comprehension disorder called Wernicke's aphasia, where speech can be expressed but not understood coherently.
• evaluation of localisation of function - 2 strengths, 2 weaknesses.

  • strength - brain scan evidence.
  • weakness - disproving evidence.
  • strength - neurosurgical evidence.
  • weakness - individual differences.
• strength of localisation of function - brain scan evidence.

  
  

  Petersen et al used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area was active during a reading task - areas of the brain have different functions. Tulving et al conducted a study of long-term memory which revealed that semantic and episodic memories reside in different areas of the prefrontal cortex. Now exists highly sophisticated and objective methods for measuring activity in the brain.
• strength of localisation of brain function - neurosurgical evidence.

  Dougherty et al reported on 44 OCD patients who had undergone a neurosurgical procedure that involves lesioning the cingulate gyrus - after 32 weeks, at post-surgery follow up, 1/3 had met the criteria for a successful response to the surgery, and 14% for a partially successful response = demonstrated that symptoms and behaviours associated with serious mental disorders like OCD are localised.  
• weakness of localisation of function - disproving evidence.

  The claim that functions are localised has been criticised - Lashley proposed the equipotentiality theory which suggests that basic motor and sensory functions are localised, but that higher mental functions are not. He claimed that intact areas of the cortex could learn to take responsibility for specific cognitive functions following brain injury.
• weakness of localisation of function - individual differences.

  Herasty found that women have proportionally larger Broca's and Wernicke's areas than men, which can explain the greater ease of language amongst women - unable to generalise research examining localisation of function to males and females equally due to different brain structures.
• hemispheric lateralisation


  the idea that the 2 halves of the brain are functionally different and that each hemisphere has functional specialisations. For example, the left is dominant for language while the right excels at visual and motor tasks.
• functions of the left brain

  • language.
  • controls the right hand.
  • receives information from the right visual field.
• functions of the right brain

  • visual and motor tasks.
  • controls the left hand.
  • receives information from the left visual field.
• how are the 2 hemispheres of the brain connected?

  nerve fibres called the corpus callosum which facilitate interhemispheric communication.
• where did split-brain research originate from?

  a treatment for severe epilepsy, where surgeons cut the corpus callosum which meant interhemispheric communication was cut off - information from one hemisphere has no way of travelling to the other and can only be processed in the hemisphere that received it.
• Key study: Sperry and Gazzaniga (aim)


  to examine the extent to which the two hemispheres are specialised for certain functions.
• Key study: Sperry and Gazzaniga (method)


  conducted many experiments including:

  • describe what you see - picture presented to left and right visual field.
  • tactile test - objects placed in the left and right hand.
  • drawing task - picture presented to the left and right visual field and asked to draw.
• Key study: Sperry and Gazzaniga (findings of describe what you see task)

  • picture presented to LVF (processed in right hemisphere) - patient could not describe what they saw and often reported seeing nothing because language is dominant in left hemisphere.
  • picture presented to RVF (processed in left hemisphere) - patient could describe what they saw.
• Key study: Sperry and Gazzaniga ( findings of tactile test)

  • objects placed in left hand - patient could not describe what they felt and could only make guesses BUT they could identify an object by selecting a similar appropriate object from a series of other objects.
  • objects placed in right hand - patient could verbally describe what they felt and could also identify the object by selecting a similar appropriate object.
• Key study: Sperry and Gazzaniga (findings of drawing task)


  • picture presented to LVF - left hand would consistently draw clearer and better pictures even though all split-brain patients were right handed = superiority of right hemisphere in motor and visual tasks.
  • picture presented to RVF - right hand would attempt to draw a picture but it was never as clear as the left hand.
• evaluation of hemispheric lateralisation

  strength: increases neural processing capacity for the ability to multi-task.

  weakness: opposing evidence on language.

  strength: sophisticated and well controlled procedure.

  consideration: lateralisation of function changes with normal ageing.
• strength of hemispheric lateralisation: increases neural processing capacity for the ability to multi-task


  Rogers et al found that in domestic chickens, lateralisation is associated with an enhanced ability to perform 2 tasks simultaneously using only one hemisphere to engage in a task, leaving the other hemisphere free to engage in other functions. For example, finding food and being vigilant for predators = provides evidence for the advantages of lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks.
• weakness of hemispheric lateralisation: opposing evidence on language.

  language may not be restricted to the left hemisphere - Turk et al discovered a patient that suffered damage to the left hemisphere, but developed the capacity to speak in the right hemisphere, leading to the ability to speak about information located on either side of the brain = suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.
• strength of hemispheric lateralisation: sophisticated and controlled procedure.

  Sperry's procedure was sophisticated in relation to how the information was visually presented - fixed point that flashed an image for only 0.1 seconds to ensure information was only processed by the opposite hemisphere, meaning he was able to control variables within the study and ensure one hemisphere received information at a time = strength of methodology and internal validity. HOWEVER, sample of epileptics means findings cannot be widely accepted or applied to normal brains, reducing ecological validity.
• consideration of hemispheric lateralisation


  it appears to change with normal ageing - szaflarski et al found language became more lateralised to the left hemisphere with an increasing age in children or adolescents, but after 25, lateralisation decreased with each decade = difficult to know why but a possibility is that using the extra processing resources of the other hemisphere may in some way compensate for age-related declines in function.