Naish Katherine R, Obhi Sukhvinder S
Social Brain, Body and Action Lab, Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada
Social Brain, Body and Action Lab, Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada.
J Neurophysiol. 2015 Oct;114(4):2278-84. doi: 10.1152/jn.00518.2015. Epub 2015 Aug 26.
The human motor system is active not only when actions are performed but also when they are observed. Experimenters often manipulate aspects of the action or context to examine factors that influence this "mirror" response. However, little is known about the role of the observer's own top-down intentions and motivation. In this exploratory study, we investigated whether observers are able to exert conscious control over their mirror response, when they are explicitly instructed to either increase or decrease mirroring. Transcranial magnetic stimulation (TMS) was used to elicit motor-evoked potentials (MEPs) in a thumb abductor muscle as participants (n = 13) watched a video of a hand squeezing a rubber ball. The size of these MEPs, relative to the size of MEPs elicited during fixation cross observation, was taken as an index of mirroring. In an initial block of trials, participants were instructed to merely observe the actions presented. After the first block, the concept of mirroring was explained to the participants, and in the second and third blocks participants were instructed to either increase or decrease their mirror response. We did not instruct them about how to achieve this increase or decrease. Our results showed no difference in either facilitation or absolute motor excitability (i.e., nonnormalized MEP size) between the three blocks, indicating that individuals do not seem to be able to exert control over motor excitability during action observation, at least in the absence of a specific and maintained strategy.
人类运动系统不仅在执行动作时活跃，在观察动作时也同样活跃。实验者常常操控动作或情境的某些方面，以检验影响这种“镜像”反应的因素。然而，对于观察者自身自上而下的意图和动机所起的作用却知之甚少。在这项探索性研究中，我们调查了观察者在被明确指示增加或减少镜像反应时，是否能够对自己的镜像反应施加有意识的控制。当参与者（n = 13）观看一只手挤压橡胶球的视频时，使用经颅磁刺激（TMS）来诱发拇指外展肌的运动诱发电位（MEP）。这些MEP的大小相对于在注视十字观察期间诱发的MEP大小，被用作镜像反应的指标。在最初的一组试验中，参与者被指示只需观察呈现的动作。在第一组试验之后，向参与者解释了镜像反应的概念，在第二组和第三组试验中，参与者被指示增加或减少他们的镜像反应。我们没有指导他们如何实现这种增加或减少。我们的结果显示，三组试验在促进作用或绝对运动兴奋性（即未标准化的MEP大小）方面均无差异，这表明个体在动作观察期间似乎无法对运动兴奋性施加控制，至少在没有特定且持续的策略时是这样。
