A microelectrode for delivery of defined charge densities.

A procedure is described for fabricating microelectrodes of platinum-30% iridium, insulated with Epoxylite varnish and having beveled ellipsoidal tips obtained by truncating a conical tip at an angle of 30-50 degrees. The geometric surface area of the ellipsoidal facet is reproducible and easily measured. Using these electrodes, neurons in the cerebral cortex of cats have been activated without damage throughout 24 h or more of continuous stimulation at 15-30 microA and charge densities of 150-300 microC/cm2.phase.