Voluntary Control of Single Motor Unit Activity in the Extensor Digitorum Muscle

A non-invasive brain-machine interface via independent control of individual motor units

“…In these studies, the raw electrical signals measured from intramuscular electrodes were used to provide participants with visual and/or auditory neurofeedback signals on the underlying motor unit activity. Using this neurofeedback system in tasks similar to our exploration procedure, authors reported that participants were able to selectively activate individual motor units in the abductor pollicis brevis 27 , extensor digitorum 28 , and the tibialis anterior muscles 26 . Despite this initial interest in individual motor unit control, research on this topic has been surprisingly limited in the last 50 years and the extent to which individual motor units can be controlled independently remained largely unclear.…”

“…Participants were instructed to use the provided neurofeedback signals to explore covert strategies to selectively recruit different motor units -mimicking pioneering studies on individual motor unit control [26][27][28][29] -and had approximately 30 minutes to select and sort in order of controllability the 3 motor units to use in the center-out task. To guide participants in their motor unit selection, we designed an algorithm that monitored motor unit activity in real-time and suggested units showing substantial evidence of independent control.…”

“…Volitional control of individual motor units was first reported in pioneering neurofeedback studies in the 1960s and 1970s [28][29][30][31] . In these studies, the raw electrical signals measured from intramuscular electrodes were used to provide participants with visual and/or auditory neurofeedback signals on the underlying motor unit activity.…”

“…However, the recruitment order of motor units within a muscle are known to vary depending on situational factors, such as the contraction speed, contraction isotonicity, and muscle fatigue, and some muscles deemed as "multifunctional" display variability based on movement direction [18][19][20][21][22][23][24][25][26][27] . In addition, pioneering studies in neurofeedback reported that people can learn to volitionally control individual motor units belonging to the same muscle when provided with visual and/or auditory feedback linked to the units' activity [28][29][30][31] . For example, Harrison and Mortensen reported a subject that was able to learn, within an hour of training, to individually control the firing rate of 4 motor units of the tibialis anterior muscle 28 .…”

Skilled independent control of individual motor units via a non-invasive neuromuscular–machine interface

“…However, out-of-order motor unit recruitments have been observed during complex motor behaviors [16][17][18], and multidimensional descending neural drives have been shown to contribute to this flexibility [18]. In addition, pioneering studies in neurofeedback reported that people can learn to volitionally control individual motor units belonging to the same muscle when provided with visual and/or auditory feedback linked to the units' activity [19][20][21][22][23]. In particular, Harrison and Mortensen reported a subject that was able to learn, within an hour of training, to isolate and produce predetermined patterns of activity in four motor units of the tibialis anterior muscle [19].…”