School of Population Health, Discipline of Psychology, Curtin University, Perth, Western Australia, Australia.
School of Psychology and Counselling, Queensland University of Technology, Brisbane, Queensland, Australia.
J Physiol. 2021 Sep;599(18):4389-4406. doi: 10.1113/JP281849. Epub 2021 Aug 18.
Suppression of corticospinal excitability is reliably observed during preparation for a range of motor actions, leading to the belief that this preparatory inhibition is a physiologically obligatory component of motor preparation. The neurophysiological function of this suppression is uncertain. We restricted the time available for participants to engage in preparation and found no evidence for preparatory inhibition. The function of preparatory inhibition can be inferred from our findings that sensory stimulation can disrupt motor output in the absence of preparatory inhibition, but enhance motor output when inhibition is present. These findings suggest preparatory inhibition may be a strategic process which acts to protect prepared actions from external interference. Our findings have significant theoretical implications for preparatory processes. Findings may also have a pragmatic benefit in that acoustic stimulation could be used therapeutically to facilitate movement, but only if the action can be prepared well in advance.
Shortly before movement initiation, the corticospinal system undergoes a transient suppression. This phenomenon has been observed across a range of motor tasks, suggesting that it may be an obligatory component of movement preparation. We probed whether this was also the case when the urgency to perform a motor action was high, in a situation where little time was available to engage in preparatory processes. We controlled the urgency of an impending motor action by increasing or decreasing the foreperiod duration in an anticipatory timing task. Transcranial magnetic stimulation (TMS; experiment 1) or a loud acoustic stimulus (LAS; experiment 2) were used to examine how corticospinal and subcortical excitability were modulated during motor preparation. Preparatory inhibition of the corticospinal tract was absent when movement urgency was high, though motor actions were initiated on time. In contrast, subcortical circuits were progressively inhibited as the time to prepare increased. Interestingly, movement force and vigour were reduced by both TMS and the LAS when movement urgency was high, and enhanced when movement urgency was low. These findings indicate that preparatory inhibition may not be an obligatory component of motor preparation. The behavioural effects we observed in the absence of preparatory inhibition were induced by both TMS and the LAS, suggesting that accessory sensory stimulation may disrupt motor output when such stimulation is presented in the absence of preparatory inhibition. We conclude that preparatory inhibition may be an adaptive strategy which can serve to protect the prepared motor action from external interference.
在准备一系列运动动作时，皮质脊髓兴奋性会被可靠地抑制，这导致人们相信这种预备性抑制是运动准备的生理必需组成部分。这种抑制的神经生理功能尚不确定。我们限制了参与者进行准备的时间，并且没有发现预备性抑制的证据。可以从我们的发现中推断出预备性抑制的功能，即感官刺激可以在没有预备性抑制的情况下破坏运动输出，但在存在抑制时可以增强运动输出。这些发现表明，预备性抑制可能是一种策略性过程，可防止预备动作受到外部干扰。我们的发现对预备过程具有重要的理论意义。这些发现还可能具有实际意义，即可以使用声学刺激进行治疗以促进运动，但前提是该动作可以提前很好地准备。
在运动启动之前不久，皮质脊髓系统会经历短暂的抑制。这种现象在各种运动任务中都有观察到，这表明它可能是运动准备的必需组成部分。我们探究了当执行运动动作的紧迫性很高时，在几乎没有时间进行预备过程的情况下，这种情况是否也是如此。我们通过增加或减少预期时间任务中的前期限时长来控制即将进行的运动动作的紧迫性。使用经颅磁刺激（TMS；实验 1）或大声声刺激（LAS；实验 2）来检查在运动准备过程中皮质脊髓和皮质下兴奋性是如何被调节的。当运动紧迫性很高时，预备性抑制的皮质脊髓束缺失，尽管运动动作按时启动。相比之下，随着准备时间的增加，皮质下回路逐渐被抑制。有趣的是，当运动紧迫性很高时，TMS 和 LAS 均降低了运动的力和活力，而当运动紧迫性较低时则增强了运动的力和活力。这些发现表明，预备性抑制可能不是运动准备的必需组成部分。当不存在预备性抑制时，我们观察到的行为效应是由 TMS 和 LAS 引起的，这表明辅助感觉刺激在没有预备性抑制的情况下呈现时可能会破坏运动输出。我们得出的结论是，预备性抑制可能是一种适应性策略，可保护预备运动动作免受外部干扰。
