High-frequency rTMS improves facial mimicry and detection responses in an empathic emotional task

In this study, we analysed facial expression detection and facial mimicry behaviour in response to an emotional empathic task. We posited that a "simulation mechanism" may be related to emotional face detection and that this mechanism could be supported by prefrontal cortical structures. To evaluate our hypothesis, we requested 16 subjects to emotionally empathise with facial stimuli and applied high frequency repeated transcranial magnetic stimulation (rTMS) to the medial prefrontal cortex (MPFC) in order to induce an increased response to the facial expressions of emotion. To determine whether emotional content affects empathic behaviour, we also varied the stimulus valence (negative vs. positive vs. neutral faces). We found that autonomic (facial zygomatic and corrugator electromyography (EMG) subjective response) and detection (correct responses (CRs); response times (RTs)) measures were modulated by the MPFC activity. Specifically, when prefrontal structures were activated, subjects displayed an increased performance in CRs and reduced RTs for face recognition, as well as increased emotion-specific EMG responses in comparison to sham effects and control site stimulation. In fact, the zygomatic muscle was more responsive in cases of positive emotion (happiness), whereas corrugator activity was more robust during periods of negative emotion (fear, anger, disgust). However, an overall stronger effect was observed in response to negative, and potentially aversive, faces when compared with responses to positive and neutral faces. Finally, a direct correlation was found between the psychophysiological responses and detection measures. In summary, these results suggest that a "simulation mechanism" underlies emotion detection in an empathic situation that includes both EMG and behavioural responses. This mechanism appears to be supported and regulated by the MPFC area.