Task-dependent vestibular feedback responses in reaching

When reaching for an earth-fixed object during self-rotation, the motor system should appropriately integrate vestibular signals and sensory predictions to compensate for the intervening motion and its induced inertial forces. While it is well established that this integration occurs rapidly, it is unknown if vestibular feedback is processed dependent on the behavioral goal. Here, we studied whether vestibular signals evoke fixed responses with the aim to preserve the hand trajectory in space or are processed more flexibly, correcting trajectories only in task-relevant spatial dimensions. We used galvanic vestibular stimulation (GVS) to perturb reaching movements toward a narrow or a wide target. Results show that the same vestibular stimulation led to smaller trajectory corrections to the wide than the narrow target. We interpret this reduced compensation as a task-dependent modulation of vestibular feedback responses, tuned to minimally intervene with the task-irrelevant dimension of the reach. These task-dependent vestibular feedback corrections are in accordance with a central prediction of optimal feedback control theory and mirror the sophistication seen in feedback responses to mechanical and visual perturbations of the upper limb.当在自身旋转过程中抓取固定于地面的物体时，运动系统需要恰当地整合前庭信号与感觉预测，以补偿期间的运动及其诱发的惯性力。尽管学界已明确该整合过程可快速完成，但前庭反馈的处理是否依赖于行为目标仍未可知。本研究旨在探讨：前庭信号所诱发的响应究竟是为了维持手部在空间中的运动轨迹，还是会以更灵活的方式进行处理——仅在任务相关的空间维度上校正运动轨迹。我们采用直流电前庭刺激（galvanic vestibular stimulation, GVS），对朝向窄目标或宽目标的伸手动作施加扰动。结果显示，相较于窄目标，相同强度的前庭刺激对宽目标条件下的轨迹校正幅度更小。我们将这种减弱的补偿效应归因于前庭反馈响应的任务依赖性调制，该调制旨在尽可能少地干扰伸手动作的任务无关维度。这类依赖于任务的前庭反馈校正，与最优反馈控制理论（optimal feedback control theory）的核心预测相符，同时也与上肢对机械扰动与视觉扰动的反馈响应所展现出的精细调控特征相一致。