module 4

• Lateralised functions


  Some brain functions rely more on one side of the brain than the other

  
• Left hemisphere functions

  • Language / Speech
• Right hemisphere functions

  • Tone of voice / prosody
  • Face perception
  • Perceptual grouping
• Crossed (contralateral) functions

  Movement, Sensation, and Vision
• Left hemisphere contralateral functions


  • Right body movement and sensation
  • Right side vision

  
• Right hemisphere contralateral functions


  • Left body movement, sensation, vision

  
• Broca's Area

  Speech Production
• In 1861, Paul Broca described a patient who was unable to speak after damage to the left frontal lobe (Broca's area)
• Language

  Lateralised to the left hemisphere in most people
• Language functions in the left hemisphere


  • Language comprehension, speech, reading
  • Speech production
• Language and hand dominance


  No overall "dominant hemisphere"
• Language lateralisation in right-handed people

  • 95% have language in Left Hemisphere
  • 5% in right hemisphere
• Language lateralisation in left-handed people

  • 70% have language in Left Hemisphere
  • 30% in right hemisphere
• Contralateral function

  Opposite side
• Ipsilateral function

  Same side
• Primary Motor and Sensory Cortex

  Connect to contralateral (opposite) side of body
• Contralateral visual cortex

  • Left side of vision to Right hemisphere
  • Right side of vision to Left hemisphere

  
• Input to each half of retina of each eye is split so that left vision from both eyes goes to right hemisphere, and right vision from both eyes to left hemisphere

  
• Corpus Callosum

  • Connects the left and right hemispheres
  • Axons of neurons (nerve fibres) crossing to the opposite (contralateral) hemisphere
• Inter-hemispheric communication

  • Vision goes to contralateral hemisphere
  • Language in left hemisphere can report what is on right side of screen

  
• Stimuli on left of screen go to Right Hemisphere, must cross to Left Hemisphere for language to report what object was

  
• Vision goes to contralateral hemisphere, movement controlled by contralateral hemisphere, left hemisphere for language and right hand to point to object

  
• "Split Brain" - severed corpus callosum

  Surgical treatment for very severe epilepsy to stop seizure activity from spreading to the other hemisphere
• Sperry and Gazzaniga studied "split-brain" patients (1960's) which led to much knowledge about lateralisation of brain function

  
• Images flashed to left or right of screen are "seen" by only right or left hemisphere
• People can reach under screen to touch and feel objects – find them by feel
• Right hemisphere can "read" and understand words, but no speech (so no verbal report)
• Hemispheres can function independently, left hemisphere can tell what it has seen but right hemisphere can only show it (via the left hand), patient cannot say what their left hand is doing

  
• Separate "consciousness" in each hemisphere?
• Hippocampus


  • Medial temporal lobe
  • Memory formation of new episodic memories
  • Spatial navigation

  
• "H.M." had his hippocampus removed to treat epilepsy in 1953 at age 27, cured epilepsy but caused severe memory loss
• H.M. could not form new memories and recall anything from after the time of the surgery, could remember and recall things from before his surgery, could "mentally rehearse" to remember things for a few seconds, could learn new skills (but could not remember learning them)
• Memory


  Not one thing, but different components mediated by different parts of the brain
• Types of memory


  • Short-term memory
  • Long-term declarative memory (episodic and semantic)
  • Long-term procedural memory
• H.M. could learn new skills (but not remember having learnt them)
• Encoding


  Laying down new memories for long-term storage
• Retrieval


  Retrieving memories for conscious recall
• Attention and Cognitive Control

  Parietal and Prefrontal Cortex

  
• Bottom-Up processes


  Driven by external stimuli or unconscious states
• Top-Down processes


  Cognitive control or volitional choice; modulation by prior knowledge and experience