Modulation of excitability in the motor system can be observed before overt movements but also in response to covert invitations to act. We asked whether such changes can be induced in the absence of even covert motor instructions, namely, as a function of the location of the hand with reference to the body. Participants received single-pulse TMS over the motor cortex while they placed their contralateral hand (right hand in Experiment 1, left hand in Experiment 2) to the right or left of their body midline, and looked either at or away from their hand. In both experiments, greater excitability was observed when gaze was directed to the right. This finding is interpreted as a consequence of left brain lateralization of motor attention. Contrary to our expectations, we furthermore consistently observed greater excitability when gaze was directed away from the hand. To account for this finding, we introduce the concept of "surveillance attention" which, we speculate, modulates cortical gain, and thereby cortical excitability. Its function is to increase readiness to act in non-foveated regions of space. Such a process confers an advantage in environments, like those in which humans evolved, in which threatening stimuli may appear unexpectedly, and at any time.

中文翻译：

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随时准备采取行动：空间对电机系统兴奋性的影响。

可以在公开运动之前观察到电机系统中的兴奋性调节，但也可以响应公开邀请而采取行动。我们询问在没有甚至隐蔽的运动指令的情况下，是否可以根据手相对于身体的位置来诱发这种变化。参与者将对侧手（实验1中的右手，实验2中的左手）放在身体中线的右侧或左侧，并注视或远离手，在运动皮层上接受单脉冲TMS。在两个实验中，将视线指向右侧时都观察到了更大的兴奋性。该发现被解释为运动注意力的左脑偏侧化的结果。与我们的期望相反，此外，当视线从手部移开时，我们还始终观察到更大的兴奋性。为了说明这一发现，我们引入了“监视注意”的概念，我们推测它可以调节皮质增益，从而调节皮质兴奋性。它的功能是增加准备在空间的非凹陷区域行动的准备。这样的过程在诸如人类进化的环境之类的环境中具有优势，在这种环境中随时可能意外地出现威胁性刺激。