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help with distributed HH simulation

Bruce Parnas brp at neuron.arc.nasa.gov
Wed Sep 8 15:07:28 EST 1993

As the subject says, I'm working on a distributed HH simulation.  Multi-compartment,
each one HH in nature (I'm not fond of the HH model, mind you, but I have to do this).

Here's the problem:

I'm coupling compartments passively, i.e. I(k) = {v(k-1) - v(k+1)}/axial_res.

If I compute the HH model per unit area (the way the parameters are given in the
original paper), the input between compartments is too small to cause propagation.

If I normalize to the area, then Cm is ver small, 1/Cm is large and the input from
neighboring compartments is too large and the thing goes unstable, even for very
small timesteps.

In the first case, it works ok if i reduce axial_res by about 10,000
In the second case, I have to increase it by about 3000.

Neither of these scale factors is justifiable.  

Anybody have any suggestions for what might be going on here?  Or a different
way of coupling the compartments?

btw, i've run this code for a point HH model, and it works just fine. It's the
compartmental coupling that's causing the problems here.

thanx for any help.

bruce parnas
brp at psychomo.arc.nasa.gov
/usr/local/Std.Disclaimer:  The opinions expressed here are mine and
not those of NASA, but you probably could have guessed that.

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