In article <1993Nov17.200600.3879 at leland.Stanford.EDU>,
dwheeler at leland.Stanford.EDU (David Brockman Wheeler) writes:
>erwin at trwacs.fp.trw.com (Harry Erwin) wites:
>>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.
>> Do you have refs for this? I would think it is more likely to involve pre-
> synaptic mechanisms such as vesicle depletion, desensitization of the release
> machinery or downregulation of Ca++ entry pathways (eg autoreceptor feedback
> inhibition of HVA Ca++ channels.
Actually, I've seen a couple of theories on this. The books are at the office,
but Dowling proposes the Ca++ depletion theory. The problem is that habituation
is supposed to be a reaction to a lack of response on the postsynaptic side.
That requires either a messenger or a difference in the chemical environment
(i.e., Ca++ depletion and non-replenishment). I'm beginning to suspect that
all synapses habituate in the short-term, and short-term potentiation increases
the sensitivity of the post-synaptic side enough to overcome the habituation.
But who am I to say? I'm just a mathematician/systems engineer/modelling
specialist who is trying to build a model of the olfactory system that
can be trained in realtime.
Harry Erwin herwin at cs.gmu.edu
(Don't try my TRW address; management has shut down internet
access to avoid violation of the Government procurement regs.)