## calculating impedance at different frequencies

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ylzang
Posts: 27
Joined: Sun Mar 08, 2015 3:38 am

### calculating impedance at different frequencies

I am wondering how Neuron compute the impedance at different frequencies. I mean if I write the hoc code myself, Obviously I need to exert an input signal and then record the change of the membrane potential. For 0 HZ input impedance, it is easy to understand. What is the input signal for NEURON to compute the input impedance of a cell at 20 HZ for example. Is it a 20 Hz sinusoidal current wave? I am trying to simulate the efficacy of synaptic inputs at different parts of a dendrite to cause an EPSP at the soma. So transfer impedance should reflect this efficacy. However, I am not sure the transfer impedance of which frequency could best approximate this synaptic input efficacy. Thanks.
ted
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Joined: Wed May 18, 2005 4:50 pm
Location: Yale University School of Medicine
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### Re: calculating impedance at different frequencies

Impedance is calculated in the frequency domain from the Laplace transformation of the spatially discretized cable equation. As mentioned here
viewtopic.php?f=8&t=3515&p=14922
the second argument to the Impedance class's compute() method specifies whether voltage-dependent channel gating is taken into account, or whether all ion channels are treated as if they have time-invariant conductance.

The question of which frequency is most representative for a given synaptic input can only be answered empirically. Jaffe and Carnevale experimented with a range of frequencies until they found one that produced a spatial profile of transfer impedance that looked "most similar" to the plot of peak somatic epsp amplitude vs. synaptic distance from the soma.
Jaffe, D. & Carnevale, N.
Passive normalization of synaptic integration influenced by dendritic architecture
Journal of Neurophysiology, 1999, 82, 3268-3285.
You can expect that the "best" frequency will depend on the time course of synaptic conductance, but to get more specific you simply have to run a bunch of simulations and examine the results.
ylzang
Posts: 27
Joined: Sun Mar 08, 2015 3:38 am

### Re: calculating impedance at different frequencies

ted wrote:Impedance is calculated in the frequency domain from the Laplace transformation of the spatially discretized cable equation. As mentioned here
viewtopic.php?f=8&t=3515&p=14922
the second argument to the Impedance class's compute() method specifies whether voltage-dependent channel gating is taken into account, or whether all ion channels are treated as if they have time-invariant conductance.

The question of which frequency is most representative for a given synaptic input can only be answered empirically. Jaffe and Carnevale experimented with a range of frequencies until they found one that produced a spatial profile of transfer impedance that looked "most similar" to the plot of peak somatic epsp amplitude vs. synaptic distance from the soma.
Jaffe, D. & Carnevale, N.
Passive normalization of synaptic integration influenced by dendritic architecture
Journal of Neurophysiology, 1999, 82, 3268-3285.
You can expect that the "best" frequency will depend on the time course of synaptic conductance, but to get more specific you simply have to run a bunch of simulations and examine the results.