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[Neuroscience] Re: cell numbers in hippocampus

Mathias via neur-sci%40net.bio.net (by mathiasDOTfranzius from webDELETEME.de)
Fri Jun 1 04:13:12 EST 2007


Hi Matt,

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 
recordings.
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).

cheers,
    Mathias

jonesmat wrote:
> Mathias,
> 
> 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...
> 
> Cheers,
> 
> Matt
> 
> 
> 
> 
> 


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