in the spinal canal electrode array 40 is implanted outside dura 21 ir emitter 42 is centrally positioned on optical axis 125 electrodes 41 l and 41 r are positioned toward the dura and within an operational range of target cells 19 photodetectors 43 l and 43 r are positioned within an operational range of spinal cord 20 target cells 19 are positioned within spinal cord 20 in an arbitrary but constant position with respect to the spinal cord in operation ir emitter 42 produces light ray 48 which forms an angle 121 with optical axis 125 light ray 48 is reflected from spinal cord 20 and enters photodetector 43 r thereby producing an electrical current ir emitter 42 also produces light ray 49 which forms angle 122 with optical axis 125 light ray 49 is reflected from spinal cord 20 and enters photodetector 43 l thereby producing an electric current an electric field produced by electrode 41 r is produced reaching target cells 19 similarly an electric field produced by electrode 41 l is produced reaching target cells 19 amplitudes a l and a r are the current to drive both the left and the right electrode respectively both are relatively high light ray 48 traverses a distance d 1 between ir emitter 42 and.