Transcranial magnetic stimulation modulates left premotor cortex activity in facial expression recognition as a function of anxiety level

Recognition of emotional facial expressions is based on simulation and mirroring processes, and the premotor cortex is supposed to support this simulation mechanism. The role of this prefrontal area in processing emotional faces with different valence (anger, fear, happiness and neutral) was explored taking into account the effect of the lateralization model (more right-side activation for negative emotions; more left-side activation for positive emotions) of face processing and anxiety level (high vs low). High-frequency repetitive transcranial magnetic stimulation (rTMS, 10 Hz) was applied to the left prefrontal area to induce an increased activation response within the left premotor cortex. Twenty-nine subjects, who were divided into two different groups depending on their anxiety level (high/low anxiety; State-Trait-Anxiety Inventory (STAI), were asked to detect emotion / no emotion. Accuracy (AcI) and response times (RTs) were considered in response to the experimental conditions. A general significant increased performance was found in response to positive emotions in the case of left-side stimulation. Moreover, whereas high-anxiety subjects revealed a significant negative-valence bias in absence of stimulation, they showed a more significant AcI increasing and RTs decreasing in response to positive emotions in case of left premotor brain activation. The present results highlight the role of the premotor system for facial expression processing as a function of emotional type, supporting the existence of a valence-specific lateralized system within the prefrontal area. Finally, a sort of “restoring effect” induced by TMS was suggested for high-anxiety subjects.