Are you looking at me? Mu suppression modulation by facial expression direction

Although we encounter numerous expressive faces on a daily basis, those that are not aimed at us will often be disregarded. Facial expressions aimed at our direction appear far more relevant and evoke an engaging affective experience, while the exact same expressions aimed away from us may not. While the importance of expression directionality is intuitive and commonplace, the neural mechanisms underlying this phenomenon are largely unknown. In the current study we measured EEG mu rhythm suppression, an established measure of mirror neuron activity, while participants viewed short video clips of dynamic facial expressions. Critically, the videos portrayed facial emotions which turned towards or away from the viewer, thus manipulating their degree of social relevance. Mirroring activity increased as a function of social relevance such that expressions turning toward the viewer resulted in increased sensorimotor activation (i.e., stronger mu suppression) compared to identical expressions turning away from the viewer. Additional analyses confirmed that expressions turning toward the viewer were perceived as more relevant and engaging than expressions turning away from the viewer, a finding not explained by perceived intensity or recognition accuracy. Mirror sensorimotor mechanisms may play a key role in determining the relevance of perceived facial expressions.