Iacullo Carly, Diesburg Darcy A, Wessel Jan R
Department of Psychological and Brain Sciences, University of Iowa, 376 Psychological and Brain Sciences Building, 340 Iowa Avenue, Iowa City, IA, 52240, USA.
Department of Neurology, University of Iowa Hospitals and Clinics, Iowa City, IA, USA.
Exp Brain Res. 2020 Dec;238(12):2701-2710. doi: 10.1007/s00221-020-05919-3. Epub 2020 Sep 19.
Motor inhibition is a key control mechanism that allows humans to rapidly adapt their actions in response to environmental events. One of the hallmark signatures of rapidly exerted, reactive motor inhibition is the non-selective suppression of cortico-spinal excitability (CSE): unexpected sensory stimuli lead to a suppression of CSE across the entire motor system, even in muscles that are inactive. Theories suggest that this reflects a fast, automatic, and broad engagement of inhibitory control, which facilitates behavioral adaptations to unexpected changes in the sensory environment. However, it is an open question whether such non-selective CSE suppression is truly due to the unexpected nature of the sensory event, or whether it is sufficient for an event to be merely infrequent (but not unexpected). Here, we report data from two experiments in which human subjects experienced both unexpected and expected infrequent events during a two-alternative forced-choice reaction time task while CSE was measured from a task-unrelated muscle. We found that expected infrequent events can indeed produce non-selective CSE suppression-but only when they occur during movement initiation. In contrast, unexpected infrequent events produce non-selective CSE suppression relative to frequent, expected events even in the absence of movement initiation. Moreover, CSE suppression due to unexpected events occurs at shorter latencies compared to expected infrequent events. These findings demonstrate that unexpectedness and stimulus infrequency have qualitatively different suppressive effects on the motor system. They also have key implications for studies that seek to disentangle neural and psychological processes related to motor inhibition and stimulus detection.
运动抑制是一种关键的控制机制，它使人类能够根据环境事件迅速调整自己的行为。快速施加的反应性运动抑制的一个标志性特征是皮质脊髓兴奋性（CSE）的非选择性抑制：意外的感觉刺激会导致整个运动系统的CSE受到抑制，即使是在不活动的肌肉中也是如此。理论表明，这反映了抑制控制的快速、自动和广泛参与，有助于行为适应感觉环境中的意外变化。然而，这样的非选择性CSE抑制是否真的是由于感觉事件的意外性质，或者仅仅是事件不频繁（但并非意外）就足够了，这还是一个悬而未决的问题。在这里，我们报告了两项实验的数据，在双选强制选择反应时任务中，人类受试者经历了意外和预期的不频繁事件，同时从与任务无关的肌肉测量CSE。我们发现，预期的不频繁事件确实可以产生非选择性CSE抑制——但只有当它们在运动开始时发生时才会如此。相比之下，意外的不频繁事件即使在没有运动开始的情况下，相对于频繁的预期事件也会产生非选择性CSE抑制。此外，与预期的不频繁事件相比，由意外事件引起的CSE抑制发生的潜伏期更短。这些发现表明，意外性和刺激不频繁对运动系统具有质的不同的抑制作用。它们对于试图区分与运动抑制和刺激检测相关的神经和心理过程的研究也具有关键意义。
