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 applied through each one of the four tripoles of the cuff as single pulses of 10 µsec 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) muscles. The torque developed in tbc ankle was simultaneously measured by means of a purposely designed apparatus. Recruitment curves were constructed for the CMAP of the GM and TA muscles and for the torque. Results: In all nerves evaluated stimulation through one or two of the tripoles initially evoked a dorsiflexion with parallel recruitment of the TA muscle at low stimulation intensity; at higher stimulation amplitude activation of the tibial innervated muscles prevailed and led to predominant plantarflexion. On the other hand, stimulating through the other two or three tripoles 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 steering currents were more noticeable with pulses of 80 % than 40 % of threshold value, and when applied from an opposite than from an adjacent anode. Conclusions: Despite the relative small size of the rat sciatic nerve and the close apposition of tibial and peroneal fascicles, we proved the feasibility of using multipolar polyimide cuff electrodes to produce selective fascicular nerve stimulation.