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A computational study of how an α-to γ-motoneurone collateral can mitigate velocity-dependent stretch reflexes during voluntary movement

Proceedings of the National Academy of Sciences - August 2024

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Muscle velocity and length signals from the spindle are useful for localizing our body in space, coordinating limb movements, and adapting to environmental changes. However, unmodulated spindle signals from lengthening muscles (i.e., stretch reflexes) disrupt arm movements. We quantified disruptions to arm movements caused by unmodulated stretch reflexes and found that they are large, variable, and movement-dependent. But, these disruptions were greatly reduced when modulating the stretch reflex gain as idealized alpha-gamma co-activation and our proposed mechanism through an alpha collateral projection to gamma motorneurone. In this example video, the arm receives feedforward movement commands and moves to a certain location in 3D space and when closing the feedback loop with unmodulated stretch reflexes, the arm movement is disrupted from the initial trajectory. In the next simulation, modulating the stretch reflex gain via the alpha-to-gamma motorneurone collateral projection or per idealized alpha-gamma co-activation allows the arm to follow the same trajectory as during movement with only feedforward commands. Such alpha-to-gamma motorneurone collateral projections provide a spinal-level mechanism that could be critical for learning, adaption, and performance via supraspinal mechanisms.

Citation

Niyo, G., Almofeez, L. I., Erwin, A., & Valero-Cuevas, F. J. (2024). A computational study of how an α-to γ-motoneurone collateral can mitigate velocity-dependent stretch reflexes during voluntary movement. Proceedings of the National Academy of Sciences, 121(34), e2321659121.

Funding

This work is supported in part by the NIH (R01 AR-050520, R01 AR-052345, and R21-NS113613), DOD CDMRP Grant MR150091, DARPA-L2M program Award W911NF1820264, NSF CRCNS Japan-US 2113096 to F.J.V.-C. and fellowships from the USC Viterbi School of Engineering to G.N. and L.I.A. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH, NSF, DoD, or DARPA.

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