Spike-accomodation in the hippocampus

Thomas Chimento chimento at ursa.arc.nasa.gov
Wed Feb 23 17:14:19 EST 1994


In article <kisley.761862839 at spot.Colorado.EDU>, kisley at spot.Colorado.EDU (Michael Kisley) writes:
|> In response, I have two comments:  
|> 
|> First of all, I have seen no such
|> clear demarcation between "accomodation" and "adaptation" in the
|> literature.  Guyton's "Textbook of Medical Physiology" does seem to favor
|> your categorization, but the problem is this:  It seems to me that when
|> people speak of "adaptation" they are usually using it to describe
|> primary sensory receptors (ie. somatosensory and olfactory receptors)
|> rather than, say, cortical pyramidal cells.  It is clear from the responses
|> I received to this post that many researchers refer to decreased spiking
|> in the hippocampus as accomodation.

Within primary sensory receptors, such as in the auditory system, the locus
of adaptation has not been isolated. Assumptions and models have placed it
both presynaptically(rundown of neurotransmitter from the immediate
stores)and postsynaptically (many sources such as transmitter binding to
receptors but in a non-open state). 

|> 
|> Secondly, I have seen no other attempt to explain "adaptation" by any other
|> mechanism than exactly your definition of "accomodation" (which is the
|> change of threshold due to depolarization).  In other words, as far as I
|> know, the slow rise in threshold due to depolarization is exactly
|> what causes spiking to decrease and eventually cease during a non-novel
|> stimulus.  Therefore, accomodation of threshold is precisely what
|> produces accomodation of spiking (or adaptation by your definition).
|> Given this, I see no reason not to refer to "adaptation" as "accomodation
|> of spiking".

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.

|> 
|> Michael Kisley
|> kisley at spot.colorado.edu

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