Three-electrode systems monopolar recording

A tissue volume zone proximal to M, with gradually reduced contribution (sensitivity) at increasing distance from M. 

Negative sensitivity in parts of the volume between the R and C electrodes. 

One interesting feature with this circuit is that if there is a capacitively coupling of 50/60 Hz mains leakage current to the patient, the necessary AC current is supplied by the current-carrying counter electrode. This current is supplied by the opamp. 

If the geometry is fixed, the electrodes included, the R and the C wires may be swapped with no change in measured admittance (reciprocity). This is an important circuit quality test. The polarization impedance of C and the impedance of R should not infiuence the results, but if any of the electrodes are too small that electrode may be in the nonlinear region so that the reciprocity test fails. 

Example Intracellular Voltage Clamp, Three-Electrode 

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