A thin-film multichannel electrode for muscle recording and stimulation in neuroprosthetics applications.

Objective. We propose, design and test a novel thin-film multichannel electrode that can be used for both recording from and stimulating a muscle in acute implants. Approach. The system is built on a substrate of polyimide and contains 12 recording and three stimulation sites made of platinum. The structure is 420 mu m wide, 20 mu m thick and embeds the recording and stimulation contacts on the two sides of the polyimide over an approximate length of 2cm. We show representative applications in healthy individuals as well as tremor patients. The designed system was tested by a psychometric characterization of the stimulation contacts in six tremor patients and three healthy individuals determining the perception threshold and current limit as well as the success rate in discriminating elicited sensations (electrotactile feedback). Also, we investigated the possibility of using the intramuscular electrode for reducing tremor in one patient by electrical stimulation delivered with timing based on the electromyographic activity recorded with the same electrode. Main results. In the tremor patients, the current corresponding to the perception threshold and the current limit were 0.7 +/- 0.2 and 1.4 +/- 0.7 mA for the wrist flexor muscles and 0.4 +/- 0.2 and 1.5 +/- 0.7 mA for the extensors. In one patient, closed-loop stimulation resulted in a decrease of the tremor power >50%. In healthy individuals the perception threshold and current limits were 0.9 +/- 0.6 and 2.1 +/- 0.6 mA for the extensor carpi raclialis muscle. The subjects could distinguish four or six stimulation patterns (two or three stimulation sites x two stimulation current amplitudes) with true positive rate >80% (two subjects) and >60% (one subject), respectively. Significance. The proposed electrode provides a compact multichannel interface for recording electromyogram and delivering electrical stimulation in applications such as neuroprostheses for tremor suppression and closed-loop myoelectric prostheses.