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

• 成果类型: Article
• 署名作者: Niyo, Grace; Almofeez, Lama I.; Erwin, Andrew; Valero-Cuevas, Francisco J.
• 署名单位: University of Southern California; University of Southern California; University System of Ohio; University of Cincinnati
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-9513
• DOI: 10.1073/pnas.2321659121
• 发表日期: 2024-08-20
• 关键词: optimal feedback-control; motor primitives; muscle-spindle; neural-control; models; position; ORGANIZATION; locomotion; MODULES; tendon

摘要

The primary motor cortex does not uniquely or directly produce alpha motoneurone (alpha-MN) drive to muscles during voluntary movement. Rather, alpha- MN drive emerges from the synthesis and competition among excitatory and inhibitory inputs from multiple descending tracts, spinal interneurons, sensory inputs, and proprioceptive afferents. One such fundamental input is velocity- dependent stretch reflexes in lengthening muscles, which should be inhibited to enable voluntary movement. It remains an open question, however, the extent to which unmodulated stretch reflexes disrupt voluntary movement, and whether and how they are inhibited in limbs with numerous multiarticular muscles. We used a computational model of a Rhesus Macaque arm to simulate movements with feedforward alpha- MN commands only, and with added velocity- dependent stretch reflex feedback. We found that velocity- dependent stretch reflex caused movement- specific, typically large and variable disruptions to arm movements. These disruptions were greatly reduced when modulating velocity- dependent stretch reflex feedback (i) as per the commonly proposed (but yet to be clarified) idealized alpha- gamma (alpha-gamma) coactivation or (ii) an alternative alpha- MN collateral projection to homonymous gamma- MNs. We conclude that such alpha- MN collaterals are a physiologically tenable propriospinal circuit in the mammalian fusimotor system. These collaterals could still collaborate with alpha-gamma coactivation, and the few skeletofusimotor fibers (beta-MNs) in mammals, to create a flexible fusimotor ecosystem to enable voluntary movement. By locally and automatically regulating the highly nonlinear neuro- musculo- skeletal mechanics of the limb, these collaterals could be a critical low- level enabler of learning, adaptation, and performance via higher- level brainstem, cerebellar, and cortical mechanisms.