Table_2_Reduced Mu Power in Response to Unusual Actions Is Context-Dependent in 1-Year-Olds.DOCX

During social interactions infants predict and evaluate other people’s actions. Previous behavioral research found that infants’ imitation of others’ actions depends on these evaluations and is context-dependent: 1-year-olds predominantly imitated an unusual action (turning on a lamp with one’s forehead) when the model’s hands were free compared to when the model’s hands were occupied or restrained. In the present study, we adapted this behavioral paradigm to a neurophysiological study measuring infants’ brain activity while observing usual and unusual actions via electroencephalography. In particular, we measured differences in mu power (6 – 8 Hz) associated with motor activation. In a between-subjects design, 12- to 14-month-old infants watched videos of adult models demonstrating that their hands were either free or restrained. Subsequent test frames showed the models turning on a lamp or a soundbox by using their head or their hand. Results in the hands-free condition revealed that 12- to 14-month-olds displayed a reduction of mu power in frontal regions in response to unusual and thus unexpected actions (head touch) compared to usual and expected actions (hand touch). This may be explained by increased motor activation required for updating prior action predictions in response to unusual actions though alternative explanations in terms of general attention or cognitive control processes may also be considered. In the hands-restrained condition, responses in mu frequency band did not differ between action outcomes. This implies that unusual head-touch actions compared to hand-touch actions do not necessarily evoke a reduction of mu power. Thus, we conclude that reduction of mu frequency power is context-dependent during infants’ action perception. Our results are interpreted in terms of motor system activity measured via changes in mu frequency band as being one important neural mechanism involved in action prediction and evaluation from early on.

在社会互动过程中，婴儿会对他人的行为进行预测与评估。过往行为研究表明，婴儿对他人行为的模仿依赖于这类评估，且具有情境依赖性：相较于示范者双手被占用或受限的情况，1岁婴儿在示范者双手自由时，更倾向于模仿非常规行为（即用额头点亮台灯）。本研究将该行为范式适配于神经生理学实验，通过脑电图（electroencephalography）测量婴儿观察常规与非常规行为时的脑活动。具体而言，我们测量了与运动激活相关的μ节律功率（6~8 Hz）的差异。本研究采用被试间设计，让12~14月龄的婴儿观看成人示范者的视频片段：示范者的双手或处于自由状态，或被限制。后续测试片段中，示范者分别通过头部或手部操作点亮台灯或音响装置。双手自由条件下的结果显示，相较于常规且可预期的手部操作行为，12~14月龄婴儿在观察非常规且出乎预料的头部操作行为时，其大脑额叶区域的μ节律功率出现下降。该现象可通过响应非常规行为时，为更新先前行为预测所需的运动激活增强来解释，不过也可考虑基于一般性注意或认知控制过程的其他解释。而在双手受限条件下，不同行为结果对应的μ频段反应并无显著差异。这意味着，相较于手部操作行为，非常规的头部操作行为未必会引发μ节律功率下降。据此我们得出结论：婴儿在行为感知过程中，μ频段功率的下降具有情境依赖性。本研究将通过μ频段变化测得的运动系统活动，解读为早期参与行为预测与评估的重要神经机制之一。