Foundations of Learning & Memory

• Baseline activity


  A neuron's activity without stimulation, spontaneously & randomly generates action potentials (APs)
• Neural signalling


  Change in activity relative to baseline, APs more frequent than usual or APs less frequent than usual
• Synaptic plasticity


  1. Increased activity causes short-term molecular changes

  2. Sustained increased activity causes long-term structural changes
• Short-term molecular changes


  • Increased neurotransmitter (NT) release by presynaptic axon terminal
  • Increased number of channels in postsynaptic membrane
• Long-term structural changes


  • Growth of new synapses
  • Synaptic take-over
• Optimising existing behaviour


  • Increased transmission rate: react more quickly / reliably to important changes in the environment
  • Decreased transmission rate: better able to ignore unimportant changes in the environment
• Acquiring new behaviour


  • Growth of new synapses: combine information from previously unrelated sources
  • Synaptic 'take-over': 're-route' information to new pathways
• Learning


  Forming new connections
• No specific place in cortex where new memories are formed or stored
• Loss of memory corresponds to size of lesion, loss of memory not specific to site of lesion
• Cortical lesions


  • Lesion in V4 may cause loss of colour perception together with loss of colour memory
  • Lesion of the right fusiform gyrus may cause loss of face perception together with loss of memory for faces
• Anterograde amnesia


  Unable to consciously remember anything new that happens, unable to learn new facts
• Retrograde amnesia


  Lose most memories of their past
• Intense negative experiences can damage our brains, especially when they combine threat and helplessness
• PTSD


  When the memory of a traumatic experience does not 'fade away' over time, but begins to dominate the patient's life
• Stress hormones may play a critical role in PTSD
• Adrenalin and Noradrenalin


  Affect memory
• Amygdala


  • Part of the limbic system, crucial for emotional memories, when damaged animals appear emotionally 'flat', no longer learn a 'fear response', over-sexed
• Hypothalamus


  Gateway from nervous to endocrine (hormonal) system
• Simplified psychobiological model of PTSD


  Fear response processed by amygdala, activates hypothalamus, activates endocrine system, releases adrenalin and noradrenalin, improves memory of stress/traumatic experience