The control and training of single motor units in isometric tasks are constrained by a common input signal
- Imperial College London, United Kingdom
- University of Freiburg, Germany
Abstract
Recent developments in neural interfaces enable the real-time and non-invasive tracking of motor neuron spiking activity. Such novel interfaces could provide a promising basis for human motor augmentation by extracting potentially high-dimensional control signals directly from the human nervous system. However, it is unclear how flexibly humans can control the activity of individual motor neurons to effectively increase the number of degrees-of-freedom available to coordinate multiple effectors simultaneously. Here, we provided human subjects (N=7) with real-time feedback on the discharge patterns of pairs of motor units (MUs) innervating a single muscle (tibialis anterior) and encouraged them to independently control the MUs by tracking targets in a 2D space. Subjects learned control strategies to achieve the target-tracking task for various combinations of MUs. These strategies rarely corresponded to a volitional control of independent input signals to individual MUs during the onset of neural activity. Conversely, MU activation was consistent with a common input to the MU pair, while individual activation of the MUs in the pair was predominantly achieved by alterations in de-recruitment order that could be explained with history-dependent changes in motor neuron excitability. These results suggest that flexible MU recruitment based on independent synaptic inputs to single MUs is unlikely, although de-recruitment might reflect varying inputs or modulations in the neuron's intrinsic excitability.
Data availability
All data generated or analysed during this study are included in the manuscript.
Article and author information
Author details
Funding
EPSRC Centre for Doctoral Training in Neurotechnology and Health
- Mario Bräcklein
H2020 NIMA (FETOPEN 899626)
- Deren Yusuf Barsakcioglu
- Jaime Ibáñez
- Jonathan Eden
- Etienne Burdet
- Carsten Mehring
- Dario Farina
H2020 TRIMANUAL (MSCA 843408)
- Jonathan Eden
- Etienne Burdet
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Human subjects: Informed consent and consent to publish was obtained from all subjects. The study was approved by the ethics committee at Imperial College London (reference number: 18IC4685).
Copyright
© 2022, Bräcklein et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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The control and training of single motor units in isometric tasks are constrained by a common input signal
eLife 11:e72871.
https://doi.org/10.7554/eLife.72871
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