Myomatrix arrays for high-definition muscle recording

Abstract

Neurons coordinate their activity to produce an astonishing variety of motor behaviors. Our present understanding of motor control has grown rapidly thanks to new methods for recording and analyzing populations of many individual neurons over time. In contrast, current methods for recording the nervous system`s actual motor output - the activation of muscle fibers by motor neurons - typically cannot detect the individual electrical events produced by muscle fibers during natural behaviors and scale poorly across species and muscle groups. Here we present a novel class of electrode devices (''Myomatrix arrays'') that record muscle activity at cellular resolution across muscles and behaviors. High-density, flexible electrode arrays allow for stable recordings from the muscle fibers activated by a single motor neuron, called a ''motor unit'', during natural behaviors in many species, including mice, rats, primates, songbirds, frogs, and insects. This technology therefore allows the nervous system's motor output to be monitored in unprecedented detail during complex behaviors across species and muscle morphologies. We anticipate that this technology will allow rapid advances in understanding the neural control of behavior and in identifying pathologies of the motor system.

An output-null signature of inertial load in motor cortex

“…All mice were implanted with optical fibers for optogenetic perturbation, and with either (1) fine wire electrodes in forelimb muscles for electromyographic (EMG) recording, (2) Myomatrix arrays 48 for high-resolution recording from motor units, or (3) silicon probes in motor cortex for neural ensemble recording. The initial surgical procedures preceding implantation of EMG or neural electrodes was similar across surgeries.…”

“…Electromyogram (EMG) recordings of gross muscle activity from the elbow flexors and extensors was made using fine-wire 32,68,69 electrodes, and recordings from single motor units were performed with both fine-wire electrodes and high-density Myomatrix arrays 48,70,71 . For each mouse, we implanted a total of four muscle locations, targeting an elbow flexor and extensor muscle on each side.…”

“…The open ends of the wire on the other side of the knot were soldered onto a 32-pin connector (Omnetics Nano, A79025, 36 pins, 4 guideposts), along with a gold pin cap for attachment to the ground (Mcmaster-Carr). Myomatrix electrodes 48 were used to only record EMG with single motor unit resolution, these electrodes had gold contacts that were plated with conductive polymer PEDOT to reduce the impedance to the measured range of 3-23 kΩ. Fine-wire electrodes were grounded with a gold pin soldered to a stainless steel wire placed through the skull and into the brain by performing a craniotomy with a dental drill ∼4 mm rostral to the forelimb area of motor cortex area.…”

I-Spin live: An open-source software based on blind-source separation for real-time decoding of motor unit activity in humans

“…Researchers classically identify a few motor units during relatively weak contractions using concentric needle or fine wire recording electrodes (4) and separate the overlapping spike trains with a template-matching algorithm (e.g., (5)). Recent developments of intramuscular (6)(7)(8)(9) and surface (3,10) EMG electrode arrays facilitate both a larger recording zone (i.e., the area from which motor unit action potentials will be recorded), and the recording of the same motor unit action potential across multiple channels. In conjunction with this hardware advance, the development of novel EMG decomposition software/programs, such as spike-sorting (11)(12)(13)(14) and blind source separation (15)(16)(17)(18)(19) algorithms, enables a relatively large number of individual motor units to be decoded from each recording (7)(8)(9)(10).…”

An information theoretic method to resolve millisecond-scale spike timing precision in a comprehensive motor program

“…To do this, we must also overcome the difficulty of obtaining spike-resolved motor unit data in a comprehensive motor circuit. Most electromyography (EMG) recordings in vertebrates either sample from too many motor units to discriminate spikes (but see [24]) or only sample single motor units with spike resolution instead of the entire motor pool, and the calcium dynamics in most imaging techniques occur over greater time-scales than the width of neural spikes. Therefore, it is difficult to compare spike timing precision in different neural circuits or muscles.…”