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

肌梭是我们感知身体位置和运动的感觉信息的主要来源。他们的输入还提供了感官反馈，以适应和纠正目标导向的运动行为。与其他躯体感觉感受器不同，肌梭的敏感性是在一个专门的运动系统（fusimotor系统）的直接控制下。然而，人类肌梭反馈的作用通常是从振动错觉和牵张反射反应中间接推断出来的。在适应性、目标导向的运动行为中，肌梭反馈是如何被调制的直接证据仍然难以捉摸。此外，关于肌梭解剖学和生理学的许多知识来自动物模型（主要是猫和猴子，也包括大鼠，蟾蜍和蛇）的研究。然而，肌梭解剖学和生理学的物种之间的差异报告危及这项动物研究的可翻译性。例如，人类肌梭表现出比在动物模型中观察到的低得多的动态和静态放电率。人类的肌梭也有更高的梭内纤维计数，理论上应该赋予他们比其他动物更大的梭运动控制。将外骨骼机器人技术与人类显微神经成像技术相结合，将使我的实验室能够量化单个肌梭活动，参与者在精确控制的刺激和任务参数下进行被动或主动运动。为了探索人类肌梭功能的基本方面，所提出的研究的主要短期目标将是从机器人控制的任务和刺激参数下的单个单元记录的大数据集构建群体平均响应估计，包括有和没有骨骼运动激活。此外，基于任务需求和行为背景的梭动系统调节肌梭反应的能力已经吸引了研究人员超过世纪，然而梭动激活独立于骨骼运动激活发生的证据，特别是在人类中，仍然不清楚且不令人信服。为了调查是否可以观察到强烈的，一致的梭动效应，反映任务的目标或执行任务的背景，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受学习任务，以及使用头戴式VR显示器将参与者暴露于虚拟高度环境。总之，结合5年的研究项目将使我能够朝着我的研究计划的长期目标取得很大进展：阐明感官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.