Flexible control of motor units: is the multidimensionality of motor unit manifolds a sufficient condition?
Author(s)
Type
Journal Article
Abstract
Understanding flexibility in the neural control of movement requires identifying the distribution of common inputs to the motor units. In this study, we identified large samples of motor units from two lower limb muscles: the vastus lateralis (VL; up to 60 motor units per participant) and the gastrocnemius medialis (GM; up to 67 motor units per participant). First, we applied a linear dimensionality reduction method to assess the dimensionality of the manifolds underlying the motor unit activity. We subsequently investigated the flexibility in motor unit control under two conditions: sinusoidal contractions with torque feedback, and online control with visual feedback on motor unit firing rates. Overall, we found that the activity of GM motor units was effectively captured by a single latent factor defining a unidimensional manifold, whereas the VL motor units were better represented by three latent factors defining a multidimensional manifold. Despite this difference in dimensionality, the recruitment of motor units in the two muscles exhibited similarly low levels of flexibility. Using a spiking network model, we tested the hypothesis that dimensionality derived from factorization does not solely represent descending cortical commands but is also influenced by spinal circuitry. We demonstrated that a heterogeneous distribution of inputs to motor units, or specific configurations of recurrent inhibitory circuits, could produce a multidimensional manifold. This study clarifies an important debated issue, demonstrating that while motor unit firings of a non-compartmentalized muscle can lie in a multidimensional manifold, the CNS may still have limited capacity for flexible control of these units.
Date Issued
2025-04-15
Date Acceptance
2025-01-27
Citation
Journal of Physiology, 2025, 603 (8), pp.2349-2368
ISSN
0022-3751
Publisher
Wiley
Start Page
2349
End Page
2368
Journal / Book Title
Journal of Physiology
Volume
603
Issue
8
Copyright Statement
© 2025 The Author(s). The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
https://www.ncbi.nlm.nih.gov/pubmed/39964831
Subjects
COMMON SYNAPTIC INPUT
DRIVE
electromyography
factor analysis
FORCE
INTERNEURONS
Life Sciences & Biomedicine
MOTONEURONS
motor neuron
muscle
MUSCLE SYNERGIES
NEURON POOLS
Neurosciences
Neurosciences & Neurology
Physiology
RECRUITMENT ORDER
RECURRENT INHIBITION
Science & Technology
SYNCHRONIZATION
synergy
Publication Status
Published
Coverage Spatial
England
Date Publish Online
2025-04-22