how to get different firing rates?

[yj232]

I've used MATLAB to do the simulation and completely new to NEURON.
I thought it should be changing the input current by using IClamp but no matter how I changed the amplitude of IClamp, the cell just spikes at a constant frequency and only the duration of spiking can be changed.
How to change the firing rate? I dont need to vary the rate during the simulation. just need the neurons to spike at 5Hz, 10Hz or 20Hz. Thanks a lot!

[ted]

Exactly what did you do to change the current delivered by the IClamp?

[yj232]

I changed the amplitude.

load_file("nrngui.hoc")
create soma

soma {
nseg = 1
insert hh
}

objectvar stim
soma stim = new IClamp(0)

stim.del = 0
stim.dur = 10000 //simulation is 10s long
stim.amp = var //var was changed but the output wasnt.

tstop = 10000


Thanks!

[ted]

So what stimulus amplitudes did you try, and what frequencies did you observe?

[yj232]

for the simplest situation as i listed up there, nseg=1 and all the parameters are default, when the amplitude is 9.73, the output is just tonic with the frequency almost 55-60 Hz, which is to fast for my simulation. And when the amplitude is 9.72, the output spikes at the same frequency for the first over 200ms and damps down to silence.
Thanks!

[ted]

The HH mechanism has a minimum frequency of repetitive firing. Below that frequency it will not generate sustained firing. Read about type 1 and type 2 spiking neurons to understand more about the difference between different kinds of f-i curves. If you want something that starts firing at a much lower frequency, you'll have to find some other mechanism than HH.

[yj232]

Thanks for clarifying that. I tried bigger amplitude of IClamp, the frequency does increase. However, the lowest spiking frequency for default parameter setting is about 55 Hz.

[yj232]

I think maybe I can modify the HH parameters to achieve this.
Where can I change the NEURON HH parameters?

[yj232]

I found the hh.mod already.

[ted]

Make sure to change the SUFFIX so your modified mechanism doesn't conflict with NEURON's built-in hh. You might want to call yours hhs, suggestive of "hh slow".