www.neuron.yale.edu

Hi.

Can somebody help me to explain the following:

I have a section with one segment with total membrane capacity of 1pF and a point process in it, that injects NONSPECIFIC_CURRENT i in the way i=gv.
I set v_init to 10mV, g is very large, let's say 1S and dt=0.1ms.

I would expect that after 0.1 ms v would reach the value of -1MV, because it would assume v to be constant over the time intervall of dt.

But instead NEURON solves correctly the equation c*v'(t)=-g*v(t) and after 0.1ms v=0mV.

How does it work? Does NEURON use variable step size per default?

Thanks

Very good question, Konstantin. NEURON's default integration method is
implicit ("backward") Euler, which has the distinct advantage that when dt is
much larger than the largest time constant in a passive system, the states of
that system reach their "infinite time" values in a single integration step. Neat, huh?

Numerical integration, as it pertains to computational modeling of neurons, is
discussed in some detail in chapter 4 of the NEURON Book
http://www.neuron.yale.edu/ftp/ted/book ... xedref.pdf
where you'll also learn why NEURON does not use the explicit/i] ("forward)
Euler method at all--unlike some other neural modeling software, which use
forward Euler by default.