Human muscle spindles and their role in guiding goal-directed motor behaviour

肌肉纺锤体是我们感知身体位置和运动的感觉信息的主要来源。它们的输入也为适应和纠正目标导向的运动行为提供了感觉反馈。与其他体感受体不同，肌纺锤体敏感性是在一个专门的运动系统（纺锤体运动系统）的直接控制下。然而，肌肉纺锤体反馈在人类中的作用通常是从振动幻觉和拉伸反射反应间接推断出来的。肌纺锤体反馈如何在适应性、目标导向运动行为中被调节的直接证据仍然难以捉摸。此外，我们对肌纺锤体解剖学和生理学的了解大多来自动物模型的研究（主要是猫和猴子，还有老鼠、蟾蜍和蛇）。然而，不同物种之间肌纺锤体解剖和生理的差异危及了动物研究的可翻译性。例如，人类肌肉纺锤体表现出的动态和静态放电率远低于在动物模型中观察到的。人类肌肉纺锤体也有更高的纤维计数，这在理论上应该赋予他们比其他动物更强的梭形运动控制能力。将外骨骼机器人技术与人体微神经摄影相结合，将使我的实验室能够量化参与者在精确控制的刺激和任务参数下被动或主动运动的单个肌肉主轴活动。为了探索人类肌肉纺锤体功能的基本方面，拟议研究的主要短期目标将是从机器人控制任务和刺激参数下的单个单元记录的大型数据集构建群体平均反应估计，包括有和没有骨骼运动激活。此外，一个多世纪以来，基于任务需求和行为背景，梭状运动系统调节肌肉纺锤体反应的能力一直引起研究人员的兴趣，然而，梭状运动激活独立于骨骼运动激活发生的证据，特别是在人类中，仍然不清楚和不令人信服。为了研究是否可以观察到反映任务目标或任务执行环境的强烈、一致的梭状运动效应，拟议研究的第二个短期目标将是使用各种实验操作来改变梭状运动激活，包括增加空间和时间任务需求，让参与者执行本体感觉学习任务，以及使用头戴式VR显示器将参与者暴露在虚拟高度环境中。综上所述，结合5年的研究项目将使我在我的研究计划的长期目标上取得良好的进展：阐明感觉反馈在目标导向的人类运动行为中的基本作用。

Muscle spindles are the primary source of sensory information underlying our perception of body position and movement. Their input also provides sensory feedback for adapting and correcting goal-directed motor behaviour. Unlike other somatosensory receptors, muscle spindle sensitivity is under the direct control of a dedicated motor system (the fusimotor system). The role of muscle spindle feedback in humans, however, is often inferred indirectly from vibratory illusions and stretch reflex responses. Direct evidence for how muscle spindle feedback is modulated during adaptive, goal-directed motor behaviour remains elusive. Furthermore, much of what is known about muscle spindle anatomy and physiology derives from research on animal models (mainly cat and monkey, also rat, toad, and snake). However, differences in muscle spindle anatomy and physiology reported between species jeopardize the translatability of this animal research. For example, human muscle spindles exhibit dynamic and static firing rates that are much lower than those observed in animal models. Human muscle spindles also have higher intrafusal fibre counts, which in theory should endow them with greater fusimotor control than other animals. Combining exoskeleton robotics with human microneurography will enable my lab to quantify single muscle spindle activity with participants passive or performing active movements under precisely controlled stimulus and task parameters. To probe basic aspects of human muscle spindle function, the primary short-term goal of the proposed research will be to construct population average response estimates from a large dataset of single unit recordings under robotically controlled task and stimulation parameters, both with and without skeletomotor activation. Additionally, the ability for the fusimotor system to modulate muscle spindle responses based on task demands and behavioural contexts has intrigued researchers for well over a century now, yet evidence for fusimotor activation occurring independently from skeletomotor activation, particularly in humans, remains unclear and unconvincing. To investigate if strong, consistent fusimotor effects can be observed that reflect the goal of a task or the context in which a task is performed, the secondary short-term goal of the proposed research will be to use various experimental manipulations for altering fusimotor activation, including increasing spatial and temporal task demands, having participants perform a proprioceptive learning task, and exposing participants to virtual height environments using a head-mounted VR display. In summary, the combined 5-year research project will enable me to make excellent progress towards the long-term goal of my research program: elucidating the fundamental role of sensory feedback in goal-directed human motor behaviour.