Blind identification of the spinal cord output in humans with high-density electrode arrays implanted in muscles

Invasive electromyography opened a new window to explore motoneuron behavior in vivo. However, the technique is limited by the small fraction of active motoneurons that can be concurrently detected, precluding a population analysis in natural tasks. Here, we developed a high-density intramuscular electrode for in vivo human recordings along with a fully automatic methodology that could detect the discharges of action potentials of up to 67 concurrently active motoneurons with 99% accuracy. These data revealed that motoneurons of the same pool receive common synaptic input at frequencies up to 75 Hz and that late-recruited motoneurons inhibit the discharges of those recruited earlier. These results constitute an important step in the population coding analysis of the human motor system in vivo.

Automated summary

Invasive electromyography has provided a new approach to study the behavior of motoneurons in vivo. However, the limitation of this technique is the inability to concurrently detect a large number of active motoneurons, which hinders population analysis in natural tasks. In this study, a high-density intramuscular electrode and a fully automatic methodology were developed to detect action potential discharges of up to 67 concurrently active motoneurons with 99% accuracy. The findings revealed the common synaptic input and inhibitory behavior of motoneurons in the same pool, which is a significant contribution to the analysis of the human motor system in vivo.