Cathodic stimulation

[Hyeon]

Hi,
I am simulating epidural cortical stimulation. For this, I made 3D computational model which represent precentral gyrus and disk type electrode was included.
For the simulation, I use COMSOL. I calculated the electric potential along the each center points of neuron segments.
Using this voltage, I stimulated neuron model by extracellullar stimulation. Referentially, I use layer 5 and layer 3 pyramidal cell from 'Mainen and Sejnowski, 1996' .

I simulated cathodic and anodic stimulation, and checked all the neurons were excited.
However, when the potential which took under the cathode electrode was applied, the neuron did not excited though I stimulated high current.

I can't sure this simulation is right. Is this phenomenon make sense?

Best regards,
angela

[ted]

Is this phenomenon make sense?

I can't say because I don't understand these two things:
1. What this is "the potential which took under the cathode electrode" ? The extracellular potential at a particular point near the cathode?
2. How did you apply it to a model cell? Did you apply the same potential to all of the segments of all of the sections in the model cell?

But aside from that, there is another thing to consider: those model cells have axons that are not based on morphometric reconstructions--their axons are just sticks whose diameters and lengths were judged to be "plausible" by the model authors. This is fine for the purpose of examining how dendritic morphology affects repetitive firing patterns, but it may not be acceptable for studying extracellular stimulation, which depends not only on the shape of the dendritic tree but also on the length, orientation, and branched architecture of the axon. For example, the modeling study by
Capogrosso et al.
Selectivity of a multi electrode array for epidural electrical stimulation of the spinal cord: a rat computational model.
poster 301.11 at the meeting of the Society for Neuroscience just two weeks ago
found that axonal morphology was the most important factor; the shape of the rest of the cell didn't matter much at all.

[Hyeon]

1. What this is "the potential which took under the cathode electrode" ? The extracellular potential at a particular point near the cathode?
yes, I calculate the potential at a particular point near the cathode.

2. How did you apply it to a model cell? Did you apply the same potential to all of the segments of all of the sections in the model cell?
First, I calculated each center points to all of the segments of all of the sections in the neuronal model. I translated the center points to be located near the electrode in my model. Then, I could calculate specific potentials in each points along neuronal models. Thus I calculated different potentials to all of the segments. Those were applied to each segments of neuronal model by extracellular stimulation.

I found that neuronal models were excited by scaling electric potentials except when I applied potentials which were calculated near the cathode.


Additionally thank you for your advise. I never know how axonal morphology is important. I have to consider it in next step. Thanks again.

[ted]

I found that neuronal models were excited by scaling electric potentials except when I applied potentials which were calculated near the cathode.

I'll have to see this for myself. Please zip up just the files that are necessary to reproduce what you observed*, and send them to
ted dot carnevale at yale dot edu

*--see
What to include in a zip file, and what to leave out
viewtopic.php?f=28&t=560

[Hyeon]

I send my code to you.
Thank you for your help.