Brain and Mind Institute, Western University, London, ON N6A5B7, Canada; Robarts Research Institute, Western University, London, ON N6A5B7, Canada; Department of Psychology, Western University, London, ON N6A5C2, Canada.
Brain and Mind Institute, Western University, London, ON N6A5B7, Canada; Department of Psychology, Western University, London, ON N6A5C2, Canada; Department of Physiology and Pharmacology, Western University, London, ON N6A5C1, Canada.
Curr Biol. 2020 May 18;30(10):1941-1948.e3. doi: 10.1016/j.cub.2020.03.005. Epub 2020 Apr 9.
Learning a new motor task modifies feedforward (i.e., voluntary) motor commands and such learning also changes the sensitivity of feedback responses (i.e., reflexes) to mechanical perturbations [1-9]. For example, after people learn to generate straight reaching movements in the presence of an external force field or learn to reduce shoulder muscle activity when generating pure elbow movements with shoulder fixation, evoked stretch reflex responses to mechanical perturbations reflect the learning expressed during self-initiated reaching. Such a transfer from feedforward motor commands to feedback responses is thought to take place because of shared neural circuits at the level of the spinal cord, brainstem, and cerebral cortex [10-13]. The presence of shared neural resources also predicts the transfer from feedback responses to feedforward motor commands. Little is known about such a transfer presumably because it is relatively hard to elicit learning in reflexes without engaging associated voluntary responses following mechanical perturbations. Here, we demonstrate such transfer by leveraging two approaches to elicit stretch reflexes while minimizing engagement of voluntary motor responses in the learning process: applying very short mechanical perturbations [14-19] and instructing participants to not respond to them [20-26]. Taken together, our work shows that transfer between feedforward and feedback control is bidirectional, furthering the notion that these processes share common neural circuits that underlie motor learning and transfer.
学习新的运动任务会改变前馈（即自愿）运动指令，这种学习也会改变对机械扰动的反馈响应（即反射）的敏感性[1-9]。例如，当人们学会在外力场中生成直线运动，或者学会在肩部固定时生成纯肘部运动时减少肩部肌肉活动后，机械扰动引起的拉伸反射反应反映了在自主发起的运动中表达的学习。这种从前馈运动指令到反馈响应的转移被认为是由于脊髓、脑干和大脑皮层水平的共享神经回路[10-13]。共享神经资源的存在也预示着从反馈响应到前馈运动指令的转移。由于在没有机械扰动后进行相关自愿反应的情况下，很难在反射中诱发学习，因此对这种转移知之甚少。在这里，我们通过利用两种方法来引出拉伸反射，同时在学习过程中最小化与自愿运动反应的参与，证明了这种转移：施加非常短的机械扰动[14-19]和指示参与者不要对它们做出反应[20-26]。总的来说，我们的工作表明前馈和反馈控制之间的转移是双向的，进一步证明这些过程共享共同的神经回路，这些回路是运动学习和转移的基础。
