A microelectrode interface is disclosed for localizing the stimulation and recording of action potentials at a portion of a nervous system. The shapes of the electrodes are such that the number of ion flux lines actually intersecting a portion of the nervous system to be stimulated is increased or even maximized. This is accomplished by choosing microelectrodes of the shape such that they are at least as large in dimension at locations away from the other microelectrode as are locations close to the other microelectrode. The microelectrodes are on one side of a chip so that it is possible to stimulate a portion of the central nervous system by placing the microelectrodes alongside the portion. By employing microelectrodes on both sides of a chip or plate, the nervous system can be stimulated in a bipolar mode as well as the unipolar mode. The microelectrode on the back side also reduces noise. A circuit is disclosed for applying current only to one or more selected pairs of microelectrodes in an array of microelectrodes. Row and column select lines, switches and multiplexers are used for passing current only between pairs of microelectrodes at selected locations in the array for stimulating a portion of a nervous system only at selected locations.