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Habituation and Conditioning

Fiberman wsun at jeeves.ucsd.edu
Sun Nov 21 17:07:08 EST 1993

In article <2c60in$l5t at truffula.fp.trw.com> erwin at trwacs.fp.trw.com (Harry Erwin) writes:
>When an afferent stimulus is repeated, but not attended to, the synapses
>involved habituate. This occurs on the presynaptic side and appears to
>involve depletion of Ca++ in the extracellular fluid at the synapse. (Ca++
>is required for vesicles to attach and release their contents.) On the
>other hand, if the stimulus is attended to, so that the post-synaptic side
>is depolarized to some degree, conditioning occurs. Is the Ca++
>concentration maintained in the synapse during conditioning? Or is the
>depletion more than counterbalanced by the conditioning process? This is a
>significant issue if one is trying to simulate learning processes in mass
>action models.
>Harry Erwin
>Internet: erwin at trwacs.fp.trw.com
>          herwin at cs.gmu.edu
>Working on Freeman nets....

Habituation could also be accounted for by another mechanism.  As
calcium enters the cell through voltage gated calcium channels,
it can activate Ca+2-dependent K+ channels.  The opening of K+
channels hyperpolarizes the membrane and shortens the spike
interval.  The best studied model for habituation is by Eric
Kandel in the Aplysia system.  However, the molecular details
have not been figured out, since he is spending more time on
facilitation and classical conditioning.  


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