Abstract
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 µm wide, 20 µm thick and embeds the recording and stimulation contacts on the two sides of the polyimide over an approximate length of 2 cm. 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 radialis muscle. The subjects could distinguish four or six stimulation patterns (two or three stimulation sites × 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.
Highlights
In rehabilitation engineering, muscle recordings are commonly used to access the neural drive of movement while electrical stimulation is applied to elicit afferent feedback
By increasing the microscopic surface area of platinum contacts with the electroplating process employed in this study, the charge injection capacity reached a value of ~500 μC cm−2 (Poppendieck et al 2009), ten times greater than the value used in the calculation of the maximal current allowed for stimulation, yielding to a further increase of the safety margin
We have shown the feasibility of using this electrode in two representative neuroprosthetic applications related to tremor reduction and sensory feedback
Summary
Muscle recordings are commonly used to access the neural drive of movement while electrical stimulation is applied to elicit afferent feedback. In myoelectric prostheses, electromyographic (EMG) signals are detected for inferring which movement an amputee intends to perform (feedforward control) (Asghari Oskoei and Hu 2007). Artificial feedback can be provided via electrical or mechanical stimulation that the subject is trained to associate to the state of the prosthesis (e.g. aperture and grasping force) (Antfolk et al 2013). Electrical stimulation has been used in neuroprostheses for tremor suppression (Prochazka et al 1992, Gallego et al 2013). In a previous study (Dosen et al 2015), we proposed a strategy that detects tremor from the electromyographic signals of the muscles originating tremor and counteracts it by applying out-of-phase electrical stimulation to the same muscles
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