Patent ID: 6988006

Claim:
An apparatus for inducing action potentials at an adjustable locus of electrically excitable tissue of an organism, comprising in combination: (A) at least one return electrode capable of being disposed within the organism; (B) a plurality of electrodes adapted to be implanted adjacent to the tissue and forming an array of a first group of electrodes in an inner ring formation and a second group of electrodes in an outer ring formation; (C) a first set of at least one electrode of the first group of electrodes capable of being driven with a first pulse; (D) a second set of at least one electrode of the second group of electrode capable of being driven with a second pulse; (E) a generator configured to provide the first and second pulses to the first and second sets with respect to the return electrode to cause a steerable electric field, and to provide a potential to cause at least one of the outer ring of electrodes to become anodal thereby causing the electric field to be contained within a certain region and causing outer tissue to be shielded from activation; and wherein the first pulse has a first begin time and a first end time and the second pulse has a second begin time and a second end time, and wherein the generator is further configured to adjust a time delay between the first end time of the first pulse and the second begin time of the second pulse, wherein the time delay determines a size and location of a suprathreshold potential area.