Evaluating current distribution on the surface of a stimulation electrode

Distribution of current on the surface of a stimulation electrode may influence distributions of effects of the stimulation in biological tissue. A method to study the current distribution at an electrode surface is described. A silver electrode in saline was imaged with a video camera during current pulses. Electrode darkening that corresponded to AgCl production by anodal current and lightening that corresponded to AgCl electrolysis by cathodal current were recorded from the video screen with phototransistors positioned on the electrode image. Inhomogeneous changes in electrode brightness were observed that indicated nonuniform current density. The method may be used to identify locations of high current on electrode surfaces.