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Suppose I set the voltage value of an isolated stimulator with a floating ground. I place one electrode above the spinal cord (positive) and the other placed subcutaneously far away from the spinal cord (negative). The circuitry within the stimulator will operate in such a way that the electrical potential difference between these two electrodes is the value I specify.

The stimulator can fix the electrical potential difference between the two electrodes in multiple ways:

  1. Hold the positive electrode's potential constant while changing the negative electrode's potential.
  2. Hold the negative electrode's potential constant while changing the positive electrode's potential.
  3. Adjusting both electrode potentials using a rule.

Although each of these ways can fix the voltage between the electrodes, they do not have equal effects on the biological environment that the electrodes are placed in. Going back to my example, if the stimulator obeys 1, I would expect a larger effect to be induced local to the spinal cord, in contrast to 2, which would would have a greater effect in the subcutaneous area. This is because there is an initial heterogenous charge distribution.

How should I assume my stimulator is fixing the potential difference between my electrodes?

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Due to charge conservation the effect will be the same independent of your configuration. You can think of this as similar to mass conservation. If you have a pipe submerged on water you can suck water from one extreme or push water in from the other extreme. In the end the flow of water is the same in both sides.

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