Localisation and function of the brain

• What is the key theoretical concept of localised brain function?

  • Specific areas of the brain are linked with specific behaviours, tasks + processes = involved in operating different parts of the body
  • Contrasts holistic view of brain that all parts are involved in processing
• What is the auditory cortex?

  • Located in temporal lobes
  • Analyses + processing = acoustic
  • Several subdivisions
  • Primary cortex involved in processing volume, pitch, tempo, etc
  • Info from left ear goes largely to right hemisphere
  • Info from right ear goes largely into left hemisphere
• What is Broca's area?

  • Located in frontal lobe in left hemisphere
  • Responsible for speech production (part of language processing)
• What is the cerebral cortex?

  • Top layer of cerebrum -> c.3-4mm
  • Holds over 10 billion nerve cells
  • Location of most higher order thinking
  • Covers both hemispheres
• What is the corpus callosum?

  • Located between left + right hemispheres
  • Thick nerve tract for communication between left + right hemispheres
  • Vital for physical movement + processing complicated info
• What is the language centre?

  • Located in left hemisphere
  • Made up of Broca's + Wernicke's areas
  • Majority of language processing happens here
• What is the motor cortex?

  • Located in both hemispheres at back of frontal lobe
  • Responsible for voluntary movements
  • Movement on right side of body processed by left hemisphere
  • Movement on left side of body processed by right hemisphere
• What is the somatosensory cortex?

  • Located at front of both parietal lobes
  • Several subdivisions
  • Processes sensory info from skin, e.g. pain, temperature, pressure, etc
  • Amount of cortex for each part of the body is proportionate to how sensitive that part is (-> how many sensory receptors are present)
• What is the visual cortex?

  • Located in occipital lobes
  • Several subdivisions
  • Processes sight-related info -> colour, shape, movement, etc
  • Info from right side of field processed by left hemisphere
  • Info from left side of field processed by right hemisphere
• What is Wernicke's area?

  • Located in temporal lobe in left hemisphere around auditory cortex
  • Responsible for comprehension of speech in language processing, e.g. understanding + assessing words
• What would happen if the motor cortex was damaged?

  Inability to move voluntarily
• What would happen if the somatosensory cortex was damaged?

  Inability to process pain, temperature, pressure, etc
• What would happen if the visual cortex was damaged?

  Blindness/a form of visual impairment
• What would happen if the auditory centres were damaged?

  Deafness/hearing loss
• When listening + speaking:

  
  

  Normal Wernicke's area:

  • Comprehends words
  • Locates word needed to convey particular meaning
  • Transmits info into Broca's area

  Damaged Wernicke's area:

  • Wernicke's aphasia/receptive aphasia
  • Cannot comprehend words heard
  • Cannot select correct words to use
  • BUT can speak fluently (talking fast but complete nonsense)
• When listening + speaking:

  
  

  Normal Broca's area:

  • Transmits motor patterns of muscle activation in vocal apparatus to motor cortex
  • = production of speech enabled

  Damaged Broca's area:

  • Broca's aphasia/expressive aphasia
  • Cannot/struggles to form spoken words
  • Long pauses
  • Far fewer words spoken
• When reading + writing:

  
  

  Normal Wernicke's area:

  • Receives words
  • From visual cortex via angular gyrus
  • Recognises words' meaning
  • Transmits info to Broca's area

  Damaged Wernicke's area:

  • Wernicke's aphasia/receptive aphasia
  • Cannot comprehend words seen or select correct words in response
  • Writing similar to speech -> motor functions working but incoherently
• When reading + writing:

  Normal Broca's area:

  • Transmits motor plans for patterns of muscle activation of hands + limbs in motor cortex
  • Production of written words enabled

  Damaged Broca's area:

  • Broca's aphasia/expressive aphasia
  • Cannot/struggles to form written words
  • Likely to produce agraphia (inability to write)
• Label the left hemisphere of the brain:

  A) motor cortex

  B) somatosensory cortex

  C) visual cortex

  D) Broca's area

  E) Wernicke's area

  F) auditory cortex

  G) arcuate fasciculus

  H) occipital lobe

  I) temporal lobe

  J) frontal lobe

  K) parietal lobe

  L) central sulcus

  M) cerebellum

  N) brain stem

  O) angular gyrus

  
• Localisation of function A&E point 1: weight of research evidence

  • Peterson et al. (1988) + Tulving et al. (1994)
  • PETs -> diff. parts of brain = diff. functions
  • Peterson et al. = Wernicke's area active in listening task, Broca's area active in reading task -> specific function related to processing diff. types of data
  • Therefore, if function was not localised these areas would not be active when performing corresponding tasks
  • Broca's case study (patient Tan, 1861) -> lesion in left frontal lobe = aphasia
  • Tan could understand spoken language but not speak coherently -> he could only say 'tan'
• Localisation of function A&E point 2: too simplistic -> lower functions may be localised but higher order functioning = holistic

  • Lashley (1950) -> equipotentiality theory (debunked) = removed 10-15% of rats' cortexes without their spatial mapping becoming impaired
  • Rats' memory issues = 50% of cortexes removed
  • Amount of damage to brain affected functioning, NOT where the damage was -> parts of brain work together to enable learning
  • Dejerine -> case study of man who lost ability to read after damaged connection between visual cortex + Wernicke's area
  • Interactionist approach needed!!
• Localisation of function A&E point 3: brain plasticity argues that seeing all functions reduced to only one part of the brain is too reductionist

  • Danelli et al. (2013) -> 2.5 y/o boy had almost full left hemisphere removed due to cancer = he regained almost all normal functions by age 17
  • Intensive rehabilitation = right hemisphere compensated for loss of language centres -> language at same level as peers with a few grammatical/naming mistakes
  • Recovery from such intense damage to brain + right hemisphere taking over Broca's + Wernicke's areas' functions undermines localisation of function