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stochastic HH

Posted: Sat Nov 24, 2007 9:31 am
Hi all,
I am using Chow&White stochastic HH neuron model (adress is below)

http://senselab.med.yale.edu/modeldb/sh ... 1&file=%5C

I couldnt define the suprathreshold input (with Iclamp)level of this model, is there anyone who help me about it
regards

Re: stochastic HH

Posted: Sat Nov 24, 2007 10:15 am
SarahJansky wrote:I couldnt define the suprathreshold input (with Iclamp)level of this model

Re: stochastic HH

Posted: Sat Nov 24, 2007 12:36 pm
ted wrote:
SarahJansky wrote:I couldnt define the suprathreshold input (with Iclamp)level of this model
No
I can add Iclamp but couldnt define the suprathreshold level of the model.
I mean : when we get the "membrane area" 1000 um2 (approx. deterministic) neuron fires for a value in Iclamp, but if we increase the area (nearest to deterministic model) it fires with another value of Iclamp. in real these values must be the same.

Also in program demo: Ik, INa are determined as (ms/cm2), but we use in Iclamp (nA), I think there is a units problem, but I couldnt cope with it,
if you examine the program you may understand what I mean.
Thanks
Regards

Re: stochastic HH

Posted: Sun Nov 25, 2007 10:12 am
SarahJansky wrote:I can add Iclamp but couldnt define the suprathreshold level of the model.
I mean : when we get the "membrane area" 1000 um2 (approx. deterministic) neuron fires for a value in Iclamp, but if we increase the area (nearest to deterministic model) it fires with another value of Iclamp. in real these values must be the same.
Not so.

Voltage-dependent channels are gated by changes of membrane potential. Bigger area
means more membrane capacitance. More membrane capacitance means more charge must
accumulate in order to produce a given change of membrane potential. If IClamp current
duration remains constant, the only way to deliver more charge is to increase the current
amplitude.
Also in program demo: Ik, INa are determined as (ms/cm2), but we use in Iclamp (nA), I think there is a units problem
"program demo" means what?
http://senselab.med.yale.edu/modeldb/sh ... odel=50391
i.e. the program in ModelDB that qualitatively replicates the findings published in Chow &
White (1996)? or do you refer to the "NEURON demo" program?

(ms/cm2) is milliseconds per square centimeter, which would be very strange units for
anything.

Perhaps you are confused about the difference between a "density mechanism" (also
called a "distributed mechanism") and what is called a "point process" in NEURON.
This is discussed in 5.6 How to specify biophysical properties in The NEURON Book;
if you don't have that, see 4.6 Density mechanisms and point processes in our paper
Hines, M.L. and Carnevale, N.T. The NEURON simulation environment.
Neural Computation 9:1179-1209, 1997.
which is available online in an enhanced version
http://www.neuron.yale.edu/neuron/papers/nc97/nctoc.htm