A method for evaluating the selectivity of electrodes implanted for nerve simulation

The authors describe a method based on the compound action potential (CAP) that provides a precise measurement of the selectivity of an electrode array and yet is relatively simple to use. The method uses the refractory interaction of the CAPs elicited by a stimulus pulse pair, along with high-resolution recording of those potentials, to achieve measurements of the selectivity of stimulation down to the scale of a few axon diameters. The feasibility of this technique is demonstrated in sciatic nerves of frogs (Rana Catesbiana) acutely implanted with a sapphire electrode array. The high-resolution recording of the compound action potential provides a method for evaluating dense neurostimulation electrode arrays. The refractory interaction of these CAP responses provides a simple method for studying current spread and electrode interaction down to a spatial resolution of about 25 mu m, depending upon the particular nerve used.