Motor neurons are the final common pathway¹ through which the brain controls movement of the body, forming the basic elements from which all movement is composed. Yet how a single motor neuron contributes to control during natural movement remains unclear. Here we anatomically and functionally characterize the individual roles of the motor neurons that control head movement in the fly, Drosophila melanogaster. Counterintuitively, we find that activity in a single motor neuron rotates the head in different directions, depending on the starting posture of the head, such that the head converges towards a pose determined by the identity of the stimulated motor neuron. A feedback model predicts that this convergent behaviour results from motor neuron drive interacting with proprioceptive feedback. We identify and genetically² suppress a single class of proprioceptive neuron³ that changes the motor neuron-induced convergence as predicted by the feedback model. These data suggest a framework for how the brain controls movements: instead of directly generating movement in a given direction by activating a fixed set of motor neurons, the brain controls movements by adding bias to a continuing proprioceptive–motor loop.

运动神经元是大脑控制身体运动的最终共同通路¹ ，形成了构成所有运动的基本元素。然而，单个运动神经元如何在自然运动过程中发挥控制作用仍不清楚。在这里，我们从解剖学和功能上描述了控制果蝇头部运动的运动神经元的个体作用。与直觉相反，我们发现单个运动神经元的活动根据头部的起始姿势向不同方向旋转头部，使得头部会聚到由受刺激的运动神经元的身份确定的姿势。反馈模型预测这种收敛行为是运动神经元驱动与本体感觉反馈相互作用的结果。我们识别并从基因上抑制²单一类别的本体感觉神经元³，它改变了反馈模型预测的运动神经元诱导的收敛。这些数据提出了大脑如何控制运动的框架：大脑不是通过激活一组固定的运动神经元直接产生给定方向的运动，而是通过向持续的本体感觉-运动循环添加偏差来控制运动。