A chronic intracortical electrode array: preliminary results

Two sets of electrode arrays made of either 25- or 50-microns-diameter Teflon-insulated platinum-iridium wire and Teflon have been developed for chronic intracortical electrical stimulation. Cortical histological studies were performed following acute and chronic implantation in cats. While some neural damage resulted from the implantations of either array configuration, a unique set of problems was associated with each diameter wire. Arrays with 50-microns electrodes and lead wires tended to maintain interelectrode spacing upon implantation, but the percutaneous leads retained residual stress which made array implantation difficult. Arrays with 25-microns electrodes and lead wires suffered from changes in interelectrode spacing upon implantation, but were much easier to manipulate during surgery. Both array configurations demonstrated some movement after implantation. It is concluded that a chronic intracortical stimulating electrode array of this geometry should have the following properties: 1) the penetrating electrodes and supporting substrate must be stiff (to maintain interelectrode spacings upon implantation), and 2) the percutaneous leads must be extremely flexible (to avoid array movement after implantation).