1.6 - Learning II Flashcards
hippocampus structure (2)
- repeated structure
- input areas on upper side (all different sensory modalities coming into one location)
long-term potentiation in the hippocampus (LTP)
prototypical mechanism underlying learning and memory
nature of connection between CA3 and CA1 neurone
plastic
how is the connection between CA1 and CA3 plastic?
- response changes when tetanus(high frequency stimulus) is applied to CA3
- when normal stimulus is applied to CA3 it illicits a much higher response from CA1 after high stimulus of CA3
what does tetanus do to the CA1/CA3 neurons that leads to LTP?
the strong simultaneous (coincident) activation of the presynaptic and postsynaptic neuron during tetanus
what does LTP depend on?
the coincidence of input neuron and output neuron
NMDA (n-methyl-d-aspartate) receptor (3)
- specific type of ionotropic glutamate receptor
- triggers movement of Na+ and K+ etc
- its biophysical properties provide means to explain LTP induction
how does NMDA act like a coincidence detector? (4)
- both glutamate-dependant and voltage-dependant
- if glutamate binds, nothing happens
- Mg2+ expelled if post synaptic neuron depolarised
- allowing it to respond to glutamate
conditions for NMDA to allow Ca2+ to enter postsynaptic neuron (2)
- presynaptic neuron must be active and release glutamate
- postsynaptic neuron must be depolarised to remove Mg2+ from the NMDA pore
how does tetanus allow Ca2+ to enter NMDA?
tetanus so strong it depolarises post-synaptic neuron leading to Mg2+ being expelled allowing Ca2+ in
Ca2+ influx triggers a molecular cascade which improves transmission by: (3)
- inserting new AMPA receptors (2nd type of ionotrpic receptor) into postsynaptic terminal
- retrograde signal improving presynaptic vesicle release (glutamate)
- transcription factor in nucleus resulting in addition of new synapses
what does the LTP mechanism underlie?
encoding of learned associations
what does LTP exhibit?
specificity and associativity
what are the most extensive studies regarding LTP?
CA3 –> CA1 glutamatergic connections in the hippocampus
what does encoding of mmeory (learning) involve?
strengthening of synaptoc connections
how is LTP useful for encoding memory (2)
- specificity - potentiation is specific to active synapses
- associativity - weak stimuli can be potentiated by simultaneous strong stimuli
John O’Keefe discovery about the hippocampus (1971) (3)
- it contains ‘cognitive map’
- pyramidal cells are place-sensitive with neurons firing in response to position of animal in space
- thus, exact same neurons that undergo LTP involved in spatial abilities
the morris water maze (2)
- rats placed in round bath of opaque water, contains single submerged (non-visible) platform
- animals swim randomly at first but with subsequent trials rapidly learn to locate platform using visual cues in test room
effect on rats in Morris water maze after NMDA receptor in hippocampus is blocked
rats exhibit no evidence of spacial learning (direct link between disruption of NMDA receptors and behavioural learning)
