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Neurophysiological processes of memory formation

1. classical conditioning - hebbian rule

   • B&C have strong link,A&C no link. so if f A and B fire at the same time then A and C will be simultaneously active & therefore the synapse between them will be strengthened
   • Bliss & Lomo, 1973 found LTP in rabbit to support the hebbian rule

2. Non exclusive ways of how LTP is expressed

   • 1)There’s an increase in the amount of neurotransmitter (glutamate) released
   • 2) There’s an increase in the number of synapses
   • 3) There’s an increase in the number of neurotransmitter receptors

3. 1) pre-synaptic neuron repeatedly fires, stimulating the postsynaptic neuron

   • Repeated glutamate excitation of AMPA receptors depolarizes (charge becomes more positive) the membrane.  The depolarization removes magnesium ions that had been blocking NMDA receptors.  Glutamate is then able to excite the NMDA receptors, opening a channel for calcium ions to enter the neuron

4. 2) The increased Ca2+ activates protein kinases (enzymes) which lead to more AMPA receptor molecules being inserted into the synaptic membrane

   • repeated activation of AMPA, change in postsynaptic membrane potential drives mg out of NMDA channels

5. 3) more transmitters - changes makesynapse more responsive making it ready to give more rapid and stronger responses because more transmitter released and there are more AMPA receptors in postsynaptic membrane

6. LTP important for - By increasing the strength/efficiency of connections between neurons it provides the molecular basis for learning,

   • happens in cortex, the cerebellum & the amygdala
   • This is necessary because, if allowed to continue increasing in strength, synapses would ultimately reach a ceiling level of efficiency, which would inhibit the encoding of new information