Axon getting stimulated even with atto Amps of current !!


I am trying to stimulate axon (SENN model) by applying external electric field of 1V. To limit the current passing through the tissue, I have increased the impedance of the tissue to make the current on the order of pA (down to aA as well). I wanted to see the threshold limit for eliciting an AP but even when the current passing through the axon is of the order of aA - it is getting stimulated which doesn't seem right to me.

I have a couple of questions -
a) Is there a better way to limit the current generated by the electrodes? If not, does my approach sound good as the voltage/current is calculated before it is being fed to the neuron and so I think it should be OK.
b) Why the Axon is still getting excited even when the current is so low?

I can share the code if someone wants to verify it quickly.

For reference, here are the screenshots for the simulations -

current plot across the axon -

AP plot along with titration sensor -


Thank you so much for your help.


@shyadav. Answering to this question require some investigation of your Sim4Life project. Could you please share with me the simulation file? Please send it to and to me in cc (

Thanks a lot,

To answer question b)
In this simulation, you have Titration enabled. This is likely to lead to a neural response because it tries to scale the EM potential field until an action potential is detected.
If you disable Titration in the simulation Setup, you will get the neural response under the effect of the potential field scaled by the modulating pulse.



Thank you for your reply.

I can understand that if you enable the titration, the software keeps on scaling the field till sees a stimulation. But it also gives us a number for the scaling field. In this case, I am seeing that number to be 0.13.

Doesn't it mean that the field has been scaled down to a factor of 0.13 to create the minimum field for stimulation - I was hoping that number to be orders of magnitude higher.

Please correct me if I am wrong.

Thanks for looking into this.