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Memory is a persistent change to large areas of the cortex

  • Memory involves most of the cortex, linked by associative systems
  • Most memories are spread across the cortex (not localised). Every time you remember something it reinforces that memory
    • Also associating digits with objects/colours etc allows you to recall them more easily
  • Destroying parts of cortex typically causes gradual degradation of memory rather than abrupt loss of unitary memories.
  • Memory persists through disruptive changes in consciousness such as sleep, coma, seizure or surgical anaesthetic.
    • This indicates that memory must involve permanent structural change in the nervous system rather than just ongoing activity patterns.
    • NB; amnesia is quite rare
    • there are permanent changes to the neurons to make memories

The physical substrate of memory is structural change in the nervous system

  • Memory is a fundamental part of nervous system
    • experience modifies the functional structure of all nervous systems
  • the act of remembering uses the same parts of cortex as when the memory was formed
  • the mechanism by which patterns of neural activity produce permanent or temporary changes in brain structure is plasticity
  • plasticity works by modifying the synapse
    • waking up quiet synapses
    • silencing active synapses
    • forming new synapses or destroying old

Hebbian learning

  • Learning occurs when two connected neurons are active simultaneously in a way that strengthens the synaptic connection


  • cells that fire together, wire together (get connected together if they're made to fire together; also your brain prunes back connections that aren't being used)
  • neurons that are out of synch, lose their link

Long term potentiation (LTP)

  • A form of synaptic plasticity
  • Discovered: in 1973 in rabbit hippocampus
    • Connections in the rabbit hippocampus could be strengthened by high frequency electrical pulses
  • Defined: a stable, long‐lasting increase in magnitude of response of hippocampal neurons after bursts of high‐frequency electrical stimulation of their afferents
    • HFS forms a memory trace in the hippocampus

Hippocampal slice preparation to test synaptic plasticity

  • Stimulate Schaffer collaterals (fibres converging on the one neuron), and then measure their target neuron
  • If you stimulate at 1 Hz, you get the same size fast EPSP, but if you stimulate it faster, you get a higher amplitude EPSP (therefore that neuron is more likely to fire in future and contribute to the overall electrical activity)

What is LTP

  • A phenomenon of the nervous system that may allow for complex behaviours such as memory and task learning
  • Formed from a combination of mechanisms that allow synapses to increase synaptic efficacy that vary in time course

  • Very hard to determine from one neuron how the whole brain is functioning
  • Increases synaptic efficacy (fast EPSP that is larger and more likely to form an AP)
  • This long term change in neuronal activity occurs in all brain structures
  • Amygdala - fear learning is strong and easy to invoke.

Does LTP = memory?

  • No, but it is part of the initial formation of memories
  • Lasts a long time
  • Labile consolidation - when you first try to invoke it, it's not stable yet (can disrupt it with a drug)