Abstract
Objective. Surface electromyography (EMG) is currently used as a control signal for active prostheses in amputees who underwent targeted muscle reinnervation (TMR) surgery. Recent research has shown that it is possible to access the spiking activity of spinal motor neurons from multi-channel surface EMG. In this study, we propose the use of multi-channel epimysial EMG electrodes as an interface for decoding motor neurons activity following TMR. Approach. We tested multi-channel epimysial electrodes (48 detection sites) built with thin-film technology in an animal model of TMR. Eight animals were tested 12 weeks after reinnervation of the biceps brachii lateral head by the ulnar nerve. We identified the position of the innervation zone and the muscle fiber conduction velocity of motor units decoded from the multi-channel epimysial recordings. Moreover, we characterized the pick-up volume by the distribution of the motor unit action potential amplitude over the epimysium surface. Main results. The electrodes provided high quality signals with average signal-to-noise ratio >30 dB across 95 identified motor units. The motor unit action potential amplitude decreased with increasing distance of the electrode from the muscle fibers (P 0.001). The decrease was more pronounced for bipolar compared to monopolar derivations. The average muscle fiber conduction velocity was 2.46 ± 0.83 m s−1. Most of the neuromuscular junctions were close to the region where the nerve was neurotized, as observed from the EMG recordings and imaging data. Significance. These results show that epimysial electrodes can be used for selective recordings of motor unit activities with a pick-up volume that included the entire muscle in the rat hindlimb. Epimysial electrodes can thus be used for detecting motor unit activity in muscles with specific fascicular territories associated to different functions following TMR surgery.
Highlights
Targeted muscle reinnervation (TMR) consists in surgically connecting the nerves that originally innervated muscles in a missing limb into those of remnant muscles above the amputation (Hoffer and Loeb 1980, Kuiken et al 2007, 2009)
We have recently demonstrated the concept of a manmachine interface based on TMR, multi-channel EMG decomposition, and mapping of motor neuron spike trains into prosthesis control (Farina et al 2017b, Kapelner et al 2018)
We investigated the use of epimysial electrodes for motor unit action potential detection in TMR muscles
Summary
Targeted muscle reinnervation (TMR) consists in surgically connecting the nerves that originally innervated muscles in a missing limb into those of remnant muscles above the amputation (Hoffer and Loeb 1980, Kuiken et al 2007, 2009). The electromyographic (EMG) signals following TMR are used for prosthesis control, usually with direct association of the EMG amplitude in a pair of reinnervated sites to the control of a prosthesis degree of freedom (Kuiken et al 2007) With this approach, the interference EMG signals represent the strength of the neural drives from the pools of reinnervating motor neurons. It has been shown that this mixture of signals can be decoded with the accurate identification of the neural sources, i.e. the motor neuron spike trains (Farina and Holobar 2016) With this approach, it is possible to directly access the spiking activity of motor neurons and thereby to establish a neural interface via the remaining stump muscles (Farina et al 2017b)
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