Lateralisation + Split Brain Research

• Areas of the brain

  red - frontal lobe

  green - parietal lobe

  purple - occipital lobe

  blue - temporal lobe

  
• hemispheres of the brain

  • the brain (aka cerebrum) split into 2 halves called hemispheres
  • some functions are controlled by a particular hemisphere - this is called lateralisation
  • as a general rule - right side of the body is controlled by left hemisphere and vice versa
• Lateralisation - motor cortex

  • located at the back of frontal lobe, next to central suculus which separates frontal and parietal lobes
  • controls voluntary muscle movement
  • is lateralised - left hemisphere controls right hand side of the body and vice versa
  • damage to this area causes a disruption in muscle movement
• Lateralisation - Broca's area

  • is a language centre
  • region in left frontal lobe
  • responsible for production of speech particularly in generating gramatically correct sentences
  • Broca's aphasia - inability to produce fluent language
• Lateralisation - Somatosensory Cortex

  • located at the front of the parietal lobe
  • receives sensory information about the skin
  • the more sensitive an area is, the more receptors there are in the brain dedicated to that area
• Lateralisation - Visual Cortex

  • located at the back of the brain in occipital lobe
  • interprets visual information
  • each eye has a left and right visual field
  • right visual field in both eyes processed in left hemisphere and vice versa
• Lateralisation - Auditory Cortex

  • found in temporal lobe
  • processes speech-based information
  • damage produces hearing loss
• Lateralisation - Wernicke's Area

  • found in left temporal lobe (below auditory cortex)
  • involved in processing language and comprehension
  • damage to this area means a struggle to comprehend language, often producing sentences that are fluent but meaningless - this is called wernicke's aphasia
• Lateralisation Eval - Evidence from neurosurgery

  • strength - damage to brin areas linked to mental disorders
  • neurosurgery is a last resort treatment for some mental disorders, targeting specific brain areas. Dougherty et al. (2002) reported on 44 people with OCD undergoing neurosurgery. At a post-surgery follow up, 30% had me the criteria for successful surgery response and 14% had shown partial response
  • This success suggests that behaviours associated with serious mental disorders may be localised.
• Lateralisation - Evidence from brain scans

  • strength - brain scans support lateralisation
  • Peterson et al. used brain scans to show how Wernicke's area was active during listening tasks and broca's area was active during reading tasks
  • this confirms localised areas for everyday behaviours, therefore objective methods for studying brain activity have provided some scientific evidence for lateralisation
• Lateralisation - Counterpoint for Brain Scan Evidence

  • weakness - Lashley (1950) challenged localisation theory
  • lashley removed areas of the cortex in rats that were learning the route through a maze. No specific area was proven to be more important than others in terms of the rat's ability to learn the route - the process of learning seemed to require every part of the cortex
  • this suggets that higher cognitive processes like learning, aren't localised.
• Lateralisation - language localisation questioned

  • weakness - Dick and Tremblay (2016) found that only 2% of researchers thought that language is solely controlled by Broca's and Wernicke's Areas
  • advanced imaging techniques like fMRIs have shown that language function is distributed far more holistically throughout the brain, so-called language streams have been identified across the cortex
  • this suggests that rather than being confined to a few areas, language may be organised more holistically in the brain, contradicting lateralisation theory