thanks for the hint! I agree that the inhibitory system probably plays a
major role in hippocampal function. I'm mainly inetersted in place field
data and try to bring together the numbers in the literature concerning
size and number of place cells in hippocampus. If I'm not completely
mistaken, most inhibitory cells in CA are identified as 'theta cells'
and pyramidal cells as 'compelx-spike cells' in electrophysiological
So my (highly questionable) calculation goes like this: In the typical
place field recording scenario an arena of less than 1m^2 is used,
average place field size is above 100cm^2, and field locations are
(mostly) homogieneously distributed in the open field. The total number
of pyramidal cells in CA1 is above 350.000, and more than 30% of all
complex-spike cells (ie pyramidal cells) in CA1 are typically active in
any given enmvironment (I'm too lazy to give all the references here,
should anyone be interested I'll do so, though).
This leads to a number of at least 1100 place cells active on average at
any given position in the experimental arena. That's interesting to
compare with the numbers estimated by Wilson stating that about 130 CA1
place cells are sufficient to estimate the animal's position with a
spatial error of less than 1cm in 1s (or 380 cells for <1cm in 0.1s).
>> Thanks for those references. They are helpful.
>> I wonder, though, if the small number of interneurons might be a bit
> deceptive, functionally.
>> They make enormous numbers of synapses onto pyramidal cells and each
> other. I think each interneuron may make tens of thousands of
> synapses, spanning several hundred microns, and contacting hundreds or
> thousands of pyramidal cells. I can't remember the exact papers where
> these things were measured in CA1, but I think this is reviewed in the
> big Freund & Buszaki "Interneurons of the Hippocampus" paper.
>> Also, Steve Cobb & Eberhard Buhl (r.i.p.) and colleagues showed that a
> single spike in a single interneuron is capable of synchronizing the
> firing of the field of pyramidal cells that it contacts.
>> Just putting in my usual plug for the importance of inhibitory
> systems. The mouse that roared, as it were...