Early Right Motor Cortex Response to Happy and Fearful Facial Expressions: A TMS Motor-Evoked Potential Study

Abstract

The ability to rapidly process others' emotional signals is crucial for adaptive social interactions. However, to date it is still unclear how observing emotional facial expressions affects the reactivity of the human motor cortex. To provide insights on this issue, we employed single-pulse transcranial magnetic stimulation (TMS) to investigate corticospinal motor excitability. Healthy participants observed happy, fearful and neutral pictures of facial expressions while receiving TMS over the left or right motor cortex at 150 and 300 ms after picture onset. In the early phase (150 ms), we observed an enhancement of corticospinal excitability for the observation of happy and fearful emotional faces compared to neutral expressions specifically in the right hemisphere. Interindividual differences in the disposition to experience aversive feelings (personal distress) in interpersonal emotional contexts predicted the early increase in corticospinal excitability for emotional faces. No differences in corticospinal excitability were observed at the later time (300 ms) or in the left M1. These findings support the notion that emotion perception primes the body for action and highlights the role of the right hemisphere in implementing a rapid and transient facilitatory response to emotional arousing stimuli, such as emotional facial expressions.

Keywords: early motor reactions; emotional facial expressions; empathic traits; motor evoked potentials; transcranial magnetic stimulation.

Figure 1

(a) Examples of visual body stimuli. (b) Trial sequence.

Figure 2

Boxplots showing MEP amplitudes recorded during the presentation of happy, neutral and fearful facial expressions at 150 and 300 ms from the stimulus onset. (a) Data from the right M1 experiment showing an early increase of MEPs for emotional facial expressions. (b) Data from the left M1 showing no MEP modulation. Asterisks denote significant Wilcoxon comparisons (p < 0.05).

Figure 3

Simple correlation between MEP contrasts at 150 ms (amplitude during happy and fearful facial expressions minus neutral conditions) and the personal distress subscale of the Interpersonal Reactivity Index.