Spike-accomodation in the hippocampus

Michael Kisley kisley at rintintin.Colorado.EDU
Thu Feb 24 11:20:08 EST 1994


chimento at ursa.arc.nasa.gov (Thomas Chimento) writes:

>You use the phrase "cease during a non-novel stimulus". This would be
>"habituation", such as the repeated poking of an Aplesia's gills with the
>eventual cessation of the withdrawl reflex. That is an entirely different
>phenomenon from adaptation, which is the reduction of a response to a
>constant stimulus. I have my doubts about your definition of accomodation,
>simply because it proposes an understanding of the mechanism underlying the
>reduction in response, and I'm not sure such an understanding really
>exists. I would like to see your operational definitions of these terms
>and then discuss if any mechanisms have been suggested.

I agree with you.  The phrase "non-novel" stimulus was intended to mean
a "constant" stimulus, as you put it.  My terminology was misleading.

On the matter of my definition of accommodation:  I have a seen a very
convincing explanation of a possible mechanism underlying spike-reduction,
namely threshold accommodation.  For instance, Ron MacGregor, using a
simplified but realistic model of a neuron shows how an accommodating
threshold can produce an "on-response" to a constant stimulus ("Neural
and Brain Modeling", MacGregor, 1987, Academic Press).  In other words,
the neuron only spikes during the onset of the stimulus.  He goes on to
show how a neuron can also spike in response to the offset of a constant
stimulus as well, and all of this with the simple mechanism of threshold
accommodation.  I admit that there is probably different mechanisms for
different cells/areas of a nervous system, but threshold accommodation
is the most convincing mechanism I've seen yet. 

Michael Kisley
kisley at magellan.colorado.edu



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