Selective fascicular stimulation of the rat sciatic nerve with multipolar polyimide cuff electrodes

Purpose: To assess a new flexible, multicontact spiral-cuff electrode made of polyimide with integrated platinum contacts for selective stimulation of nerve fascicles. Methods: Polyimide cuff electrodes with 12 Pt sites in the spiral cuff were acutely implanted around the sciatic nerve of rats. Stimulation was applie d through each one of the four tripoles of the cuff as single pulses of 10 mu sec duration of increasing intensity The motor responses were monitored from EMG recordings of gastrocnemius medialis (GM; innervated by the tibial nerve) and tibialis anterior (TA; innervated by the peroneal nerve) muscle s. The torque developed in the ankle was simultaneously measured by means o f a purposely designed apparatus. Recruitment curves were constructed for t he CMAP of the GM and TA muscles and for the torque. Results: In all nerves evaluated stimulation through one or two of the trip oles initially evoked a dorsiflexion with parallel recruitment of the TA mu scle at low stimulation intensity; at higher stimulation amplitude activati on of the tibial innervated muscles prevailed and led to predominant planta rflexion. On the other hand, stimulating through the other two or three tri poles evoked plantarflexion from the beginning, with increasing force from low to high stimulus intensity. The effectiveness of selective stimulation was mildly increased by applying a simultaneous transverse steering current . The threshold for torque dorsiflexion decreased and the dynamic range of stimulation that resulted in a net dorsiflexion expanded. The effects of st eering currents were more noticeable with pulses of 80 % than 40 % of thres hold value, and when applied from an opposite than from an adjacent anode. Conclusions: Despite the relative small size of the rat sciatic nerve and t he close apposition of tibial and peroneal fascicles, we proved the feasibi lity of using multipolar polyimide cuff electrodes to produce selective fas cicular nerve stimulation.