Simultaneous recording of EEG and facial muscle reactions during spontaneous emotional mimicry.

The perception of emotional facial expressions induces covert imitation in emotion-specific muscles of the perceiver's face. Neural processes involved in these spontaneous facial reactions remain largely unknown. Here we concurrently recorded EEG and facial EMG in 15 participants watching short movie clips displaying either happy or angry facial expressions. EMG activity was recorded for the zygomaticus major (ZM) that elevates the lips during a smile, and the corrugator supercillii (CS) that knits the eyebrows during a frown. We found increased EMG activity of CS in response to angry expressions, and enhanced EMG activity of ZM for happy expressions, replicating earlier EMG studies. More importantly, we found that the amplitude of an early visual evoked potential (right P1) was larger when ZM activity to happy faces was high, and when CS activity to angry faces was high, as compared to when muscle reactions were low. Conversely, the amplitude of right N170 component was smaller when the intensity of facial imitation was high. These combined EEG-EMG results suggest that early visual processing of face expression may determine the magnitude of subsequent facial imitation, with dissociable effects for P1 and N170. These findings are discussed against the classical dual-route model of face recognition.