The control and training of single motor units in isometric tasks are constrained by a common input signal

  1. Mario Bräcklein
  2. Deren Yusuf Barsakcioglu
  3. Jaime Ibáñez
  4. Jonathan Eden
  5. Etienne Burdet
  6. Carsten Mehring
  7. Dario Farina  Is a corresponding author
  1. Imperial College London, United Kingdom
  2. 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

  1. Mario Bräcklein

    Department of Bioengineering, Imperial College London, London, United Kingdom
    Competing interests
    Mario Bräcklein, is one inventor in a patent application (Neural interface. UK Patent application no. GB2014671.8. September 17, 2020) related to the methods and applications of this work..
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-1537-7495
  2. Deren Yusuf Barsakcioglu

    Department of Bioengineering, Imperial College London, London, United Kingdom
    Competing interests
    Deren Yusuf Barsakcioglu, is an inventor in a patent (Neural 690 Interface. UK Patent application no. GB1813762.0. August 23, 2018) and in a patent application (Neural interface. UK Patent application no. GB2014671.8. September 17, 2020) related to the methods and applications of this work..
  3. Jaime Ibáñez

    Department of Bioengineering, Imperial College London, London, United Kingdom
    Competing interests
    No competing interests declared.
  4. Jonathan Eden

    Department of Bioengineering, Imperial College London, London, United Kingdom
    Competing interests
    No competing interests declared.
  5. Etienne Burdet

    Department of Bioengineering, Imperial College London, London, United Kingdom
    Competing interests
    No competing interests declared.
  6. Carsten Mehring

    Bernstein Center Freiburg, University of Freiburg, Freiburg, Germany
    Competing interests
    No competing interests declared.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8125-5205
  7. Dario Farina

    Department of Bioengineering, Imperial College London, London, United Kingdom
    For correspondence
    d.farina@imperial.ac.uk
    Competing interests
    Dario Farina, is an inventor in a patent (Neural 690 Interface. UK Patent application no. GB1813762.0. August 23, 2018) and in a patent application (Neural interface. UK Patent application no. GB2014671.8. September 17, 2020) related to the methods and applications of this work..
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7883-2697

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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  1. Mario Bräcklein
  2. Deren Yusuf Barsakcioglu
  3. Jaime Ibáñez
  4. Jonathan Eden
  5. Etienne Burdet
  6. Carsten Mehring
  7. Dario Farina
(2022)
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

Share this article

https://doi.org/10.7554/eLife.72871

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