Less Empathic and More Reactive: The Different Impact of Childhood Maltreatment on Facial Mimicry and Vagal Regulation

Abstract

Facial mimicry and vagal regulation represent two crucial physiological responses to others' facial expressions of emotions. Facial mimicry, defined as the automatic, rapid and congruent electromyographic activation to others' facial expressions, is implicated in empathy, emotional reciprocity and emotions recognition. Vagal regulation, quantified by the computation of Respiratory Sinus Arrhythmia (RSA), exemplifies the autonomic adaptation to contingent social cues. Although it has been demonstrated that childhood maltreatment induces alterations in the processing of the facial expression of emotions, both at an explicit and implicit level, the effects of maltreatment on children's facial mimicry and vagal regulation in response to facial expressions of emotions remain unknown. The purpose of the present study was to fill this gap, involving 24 street-children (maltreated group) and 20 age-matched controls (control group). We recorded their spontaneous facial electromyographic activations of corrugator and zygomaticus muscles and RSA responses during the visualization of the facial expressions of anger, fear, joy and sadness. Results demonstrated a different impact of childhood maltreatment on facial mimicry and vagal regulation. Maltreated children did not show the typical positive-negative modulation of corrugator mimicry. Furthermore, when only negative facial expressions were considered, maltreated children demonstrated lower corrugator mimicry than controls. With respect to vagal regulation, whereas maltreated children manifested the expected and functional inverse correlation between RSA value at rest and RSA response to angry facial expressions, controls did not. These results describe an early and divergent functional adaptation to hostile environment of the two investigated physiological mechanisms. On the one side, maltreatment leads to the suppression of the spontaneous facial mimicry normally concurring to empathic understanding of others' emotions. On the other side, maltreatment forces the precocious development of the functional synchronization between vagal regulation and threatening social cues facilitating the recruitment of fight-or-flight defensive behavioral strategies.

Fig 1. Corrugator and zygomaticus EMG responses to facial expressions of positive and negative emotions.

A) Corrugator EMG activity displayed emotion by emotion for maltreated group (Mal) and control group (Con). * = p < 0.05. Error bars represent SE. B) Zygomaticus EMG activity displayed emotion by emotion for maltreated group (Mal) and control group (Con).

Fig 2. Corrugator and zygomaticus congruent EMG responses to facial expressions of emotions.

A) Mean congruent corrugator EMG activity for maltreated group (Mal) and control group (Con) during the visualization of facial expressions of negative emotions. * = p < 0.05. Error bars represent SE. B) Mean congruent zygomaticus EMG activity for maltreated group (Mal) and control group (Con) during the visualization of joy facial expressions.

Fig 3. Correlation plots between baseline and suppression RSA values in the two groups.

Plots of correlations between baseline and suppression RSA values for maltreated children (Mal) and controls (Con) displayed emotion by emotion. * = Bonferroni corrected p < 0.012.