### "Extracellular stimulation and recording" - question

Posted:

**Thu Apr 12, 2012 12:00 pm**I have a question about the Extracellular Stimulation and Recording post in the Hot Tips forum (viewtopic.php?f=28&t=168).

The post says that there are two approaches to extracellular stimulation. One is to introduce into the cable equation a current term that's equal to the second spatial derivative of the extracellular field. The second is to assume that the extracellular medium is linear, allowing someone to approximate the external field of multiple currents as
where Vo(x,y,z) is the external field at location x,y,z, Z_j is the transfer impedance to that location, and I_j is the jth current. Vo is then used to drive e_extracellular.

I'm used to implementing the first approach, and I want to contrast it with the second. The first approach calculates current; the second approach calculates extracellular field and feeds this into NEURON via e_extracellular. How does the second approach calculate membrane current though? How do I see the exact code that uses e_extracellular to calculate membrane current?

Thanks a lot.

The post says that there are two approaches to extracellular stimulation. One is to introduce into the cable equation a current term that's equal to the second spatial derivative of the extracellular field. The second is to assume that the extracellular medium is linear, allowing someone to approximate the external field of multiple currents as

Code: Select all

```
Vo(x,y,z) = SUMMA Z_j(x,y,z) I_j Eq. 1
j
```

I'm used to implementing the first approach, and I want to contrast it with the second. The first approach calculates current; the second approach calculates extracellular field and feeds this into NEURON via e_extracellular. How does the second approach calculate membrane current though? How do I see the exact code that uses e_extracellular to calculate membrane current?

Thanks a lot.