Brain and Mind Institute, Western University, London, Ontario, Canada.
Department of Physiology and Pharmacology, Western University, London, Ontario, Canada.
J Neurophysiol. 2021 Apr 1;125(4):1339-1347. doi: 10.1152/jn.00487.2020. Epub 2021 Mar 10.
Efficiently controlling the movement of our hand requires coordinating the motion of multiple joints of the arm. Although it is widely assumed that this type of efficient control is implemented by processing that occurs in the cerebral cortex and brainstem, recent work has shown that spinal circuits can generate efficient motor output that supports keeping the hand in a static location. Here, we show that a spinal pathway can also efficiently control the hand during reaching. In our first experiment, we applied multijoint mechanical perturbations to participants' elbow and wrist as they began reaching toward a target. We found that spinal stretch reflexes evoked in elbow muscles were not proportional to how much the elbow muscles were stretched but instead were dependent on the hand's location relative to the target. In our second experiment, we applied the same elbow and wrist perturbations but had participants change how they grasped the manipulandum, diametrically altering how the same wrist perturbation moved the hand relative to the reach target. We found that changing the arm's orientation diametrically altered how spinal reflexes in the elbow muscles were evoked, and in such a way that were again dependent on the hand's location relative to the target. These findings demonstrate that spinal circuits can help efficiently control the hand during dynamic reaching actions and show that efficient and flexible motor control is not exclusively dependent on processing that occurs within supraspinal regions of the nervous system. We have previously shown that spinal circuits can rapidly generate reflex responses that efficiently engage multiple joints to support postural hand control of the upper limb. Here, we show that spinal circuits can also rapidly generate such efficient responses during reaching actions.
有效地控制手部的运动需要协调手臂多个关节的运动。尽管人们普遍认为这种高效控制是通过大脑皮层和脑干中的处理来实现的，但最近的研究表明，脊髓回路可以产生高效的运动输出，以支持手部保持在静态位置。在这里，我们表明，脊髓通路也可以在伸手时有效地控制手部。在我们的第一个实验中，我们在参与者开始伸手向目标时，对他们的肘部和手腕施加多关节机械扰动。我们发现，在肘部肌肉中引发的脊髓伸展反射与肘部肌肉伸展的幅度不成比例，而是取决于手相对于目标的位置。在我们的第二个实验中，我们施加了相同的肘部和手腕扰动，但让参与者改变他们握持操纵杆的方式，使同样的手腕扰动相对于到达目标改变了手部的运动方式。我们发现，改变手臂的方向会极大地改变肘部肌肉中诱发的脊髓反射，而且这种改变方式再次取决于手相对于目标的位置。这些发现表明，脊髓回路可以帮助在动态伸手动作中有效地控制手部，并表明高效和灵活的运动控制不仅仅依赖于神经系统的中枢区域内发生的处理。我们之前已经表明，脊髓回路可以快速产生反射反应，有效地协调多个关节，以支持上肢姿势性手部控制。在这里，我们表明，脊髓回路也可以在伸手动作中快速产生这种高效的反应。
