Using voluntary motor commands to inhibit involuntary arm movements

A hallmark of voluntary motor control is the ability to stop an ongoing movement. Is voluntary motor inhibition a general neural mechanism that can be focused on any movement, including involuntary movements, or is it mere termination of a positive voluntary motor command? The involuntary arm lift, or ‘floating arm trick’, is a distinctive long-lasting reflex of the deltoid muscle. We investigated how a voluntary motor network inhibits this form of involuntary motor control. Transcranial magnetic stimulation of the motor cortex during the floating arm trick produced a silent period in the reflexively contracting deltoid muscle, followed by a rebound of muscle activity. This pattern suggests a persistent generator of involuntary motor commands. Instructions to bring the arm down voluntarily reduced activity of deltoid muscle. When this voluntary effort was withdrawn, the involuntary arm lift resumed. Further, voluntary motor inhibition produced a strange illusion of physical resistance t...自主运动控制的标志性特征之一，便是能够终止正在进行的运动。自主运动抑制究竟是一种可作用于包括不自主运动在内的任意运动的通用神经机制，还是仅仅是终止正向自主运动指令的过程？不自主抬臂现象，或称“浮臂效应”，是三角肌特有的持续性反射活动。本研究探讨了自主运动神经网络如何抑制此类不自主运动控制过程。在浮臂效应期间对运动皮层施加经颅磁刺激（Transcranial magnetic stimulation），可在反射性收缩的三角肌中引发一段静息期，随后伴随肌电活动的反弹。该现象提示存在持续性的不自主运动指令发生器。要求自主放下手臂的指令可降低三角肌的活动水平。当该自主努力被撤销后，不自主抬臂现象会再次出现。此外，自主运动抑制还会引发一种关于物理阻力的奇异错觉……