A simple netstim question

[adamimos]

I am trying to use NetStim to give a train of current injections with specified max current. I have a netcon which has a NetStim as a source, and an exp2syn as a target. My understanding is that when NetStim passes NetStim.threshold, NetStim.weight will be sent to exp2syn, which will give current as:


i = weight * some function of time normalized to a max of one * (v - e)

where e is a parameter of exp2syn, and v is the membrane potential. I am trying to think of a way in which to have some control over the current injection amount. I was wondering how exactly NetStim works. Is it a train of delta functions? How do I know what it means exactly to set a threshold of 10, or 100000. What I mean exactly is how does the value of NetStim change when it fires?

Thanks

[ted]

Questions that touch on important topics. Get ready to think new thoughts.

NetStim uses an event-driven finite-state machine, implemented with conditional logic and self-events, to generate a sequence of events that can be delivered to target mechanisms. For a reasonable definition of "finite-state machine" see Wikipedia. To begin to understand how spike-triggered synaptic transmission and artificial spiking cells are implemented in NEURON, first please throw away all guesses you may have made. Then read this paper
Hines, M.L. and Carnevale, N.T. Discrete event simulation in the NEURON environment. Neurocomputing 58-60:1117-1122, 2004.
which is available as a preprint from the Publications about NEURON page
http://www.neuron.yale.edu/neuron/nrnpubs
After that you will have a much clearer idea of how events can be used in NEURON, and you'll be able to read and understand the NMODL source code for the NetStim class, which is contained in the file netstim.mod (download the source code for NEURON, expand it, and look in nrn-x.x/src/nrnoc/ )

I am trying to use NetStim to give a train of current injections with specified max current.

If you need to generate a train of current pulses, you probably don't want to use a NetStim or any kind of synaptic mechanism. Have you examined these items

• SEClamp and IClamp just deliver rectangular step waveforms. How can I make them produce an arbitrary waveform, e.g. something that I calculated or recorded from a real cell?
  I just want a current clamp that will deliver a sequence of current pulses at regular intervals. Vector play seems like overkill for this.

in the FAQ list http://www.neuron.yale.edu/neuron/faq/general-questions ?

[adamimos]

you da man!

[ted]

But of course.