For a multicontact cuff electrode to be functional all target fascicles must be accessible. This can be achieved if there are sufficient numbers of contact to cover all possible positions of nerves inside a cuff ofr techniques must be developed to create steerable excitation sites. The development of techniques to steer (or move a virtual excitation sites) would make it possible to manufacture functional multicontact cuff type electrodes with fewer contacts, leads and simpler connectors. In the following section we show that “field steering” can be use to position an excitation site (a virtual excitation site) at a point in space where there is no actual contact in the cuff electrode.

Anodic Steering:

A comparison was made of the torque outputs produced by direct stimulation of each branch of the sciatic Sciatic nerve, labeled as Tib, MG, LG and CP, and to the torque produced by stimulation of each contact in the cuff electrode, labeled 0°, 90°, 180° and 270°, in Cat #388thea feline. Based on the torque outputs, the Tib, MG, and LG branches of the sciatic were activated by the 0°, 90°, and 180° contacts on the sciatic nerve. No single contact activated the common peroneal by itself. The addition of anodic steering current from the 0° position to the 270° position (labeled c270°a0°) was found to produce the same torque output as is was produced by stimulation of the common peroneal branch. The inset in the bottom right corner is a reconstruction of the nerve cross section and the relative locations of each contact. A schematic of the configuration used to apply current for the multiple contact stimulation is also shown.

In this experiment, no single contact activated the Medial Gastrocnemius (MG MG) by itself. The addition of cathodic steering current from the 90° position to the 180° position (labeled c90°c180°) was found to activate the MG selectively over its entire range. The inset in the top left corner is a reconstruction of the nerve cross-section and the relative locations of each contact. This schematic depicts the current configuration used to apply the steering currents.

Shown in this table are the stimulation combinations used at the level of the sciatic nerve to achieve the same torque output as each corresponding fascicle for each experiment are shown in this table. For
In each case in which the same torque output as the corresponding nerve branch was achieved, four placeholders were entered to represent how the four corresponding contacts (0°, 90°, 180° and 270°) were used.
An open circle (o) represents a contact that was not used for that particular configuration.
A minus sign (-) indicates that the corresponding contact was pulsed in the cathodic direction.
A plus sign (+) indicates that the corresponding contact was pulsed in the anodic direction.
Four filled circles (• • • •) indicate that the particular torque was not achieved fully with single contact stimulation but not targeted using steering currents due to time limitations. In no case was a particular torque not achieved when multiple contact stimulation was attempted. The shaded cells are the cases in which “collision block addition” was used to verify the corresponding fascicle was fully and selectively activated.
The results of these experiments indicate that a four contact, self-sizing, cuff electrode can be used to target activation of any one of four motor fascicles, over it entire range, provided the stimulator is capable of effecting “field steering” by the application of positive or negative currents to any of the four contacts on demand and simultaneously.

Tarler, M. D. and J. Thomas Mortimer (2003) Selective and independent activation of four motor fascicles using a four contact nerve cuff electrode. IEEE Trans. In Press