Data_Sheet_1_Does TMS Disruption of the Left Primary Motor Cortex Affect Verb Retrieval Following Exposure to Pantomimed Gestures?.docx

Previous research suggests that meaning-laden gestures, even when produced in the absence of language (i.e., pantomimed gestures), influence lexical retrieval. Yet, little is known about the neural mechanisms that underlie this process. Based on embodied cognition theories, many studies have demonstrated motor cortex involvement in the representation of action verbs and in the understanding of actions. The present study aimed to investigate whether the motor system plays a critical role in the behavioral influence of pantomimed gestures on action naming. Continuous theta burst stimulation (cTBS) was applied over the hand area of the left primary motor cortex and to a control site (occipital cortex). An action-picture naming task followed cTBS. In the naming task, participants named action pictures that were preceded by videos of congruent pantomimed gestures, unrelated pantomimed gestures or a control video with no movement (as a neutral, non-gestural condition). In addition to behavioral measures of performance, cTBS-induced changes in corticospinal activity were assessed. We replicated previous finding that exposure to congruent pantomimed gestures facilitates word production, compared to unrelated or neutral primes. However, we found no evidence that the left primary motor area is crucially involved in the mechanism underlying behavioral facilitation effects of gesture on verb production. Although, at the group level, cTBS induced motor cortex suppression, at the individual level we found remarkable variability of cTBS effects on the motor cortex. We found cTBS induction of both inhibition of corticospinal activity (with slower behavioral of responses) and enhancement (with faster behavioral responses). Our findings cast doubt on assumptions that the motor cortex is causally involved in the impact of gestures on action-word processing. Our results also highlight the importance of careful consideration of interindividual variability for the interpretation of cTBS effects.既往研究表明，即便在无语言伴随的情况下产生的表意手势（即哑剧手势，pantomimed gestures），也会对词汇提取过程产生影响。目前学界对该过程背后的神经机制仍缺乏深入了解。基于具身认知（embodied cognition）理论，多项研究已证实，运动皮层参与动作动词的表征与动作理解过程。本研究旨在探究运动系统是否在哑剧手势对动作命名的行为影响中发挥关键作用。 研究采用连续θ波爆发刺激（continuous theta burst stimulation, cTBS），分别作用于左侧初级运动皮层（left primary motor cortex）的手部代表区，以及对照位点枕叶皮层（occipital cortex）。刺激结束后，参与者需完成动作图片命名任务。在该任务中，参与者需对紧随三类先行刺激后的动作图片进行命名：分别为匹配性哑剧手势视频先行、非匹配性哑剧手势视频先行，以及无动作的对照视频先行（作为中性非手势条件）。除采集行为绩效指标外，本研究还评估了cTBS诱导的皮层脊髓活动变化。 我们重复了既往研究的发现：相较于非匹配启动或中性启动条件，匹配性哑剧手势的暴露可促进词汇产生。然而，我们未找到证据表明左侧初级运动皮层在手势对动词产生的行为促进效应机制中起到关键作用。尽管在群体水平上，cTBS可诱导运动皮层产生抑制效应，但在个体水平上，我们观察到cTBS对运动皮层的效应存在显著的个体差异。具体而言，cTBS既可诱导皮层脊髓活动的抑制（伴随行为反应时延长），也可诱导其增强（伴随行为反应时缩短）。 本研究结果对“运动皮层因果性参与手势对动作词汇加工的影响”这一假设提出了质疑。同时，本研究结果也强调，在解释cTBS效应时，需审慎考量个体间的差异性。