Right Temporoparietal Junction Modulates In-Group Bias in Facial Emotional Mimicry: A tDCS Study

Abstract

The present study employs transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, to explore the possible role of the right temporoparietal junction (rTPJ) in regulating in-group bias in facial emotional mimicry. Participants received either anodal or cathodal stimulation, or they were assigned to a sham condition. After that, they passively viewed a series of video clips depicting different emotions (happiness and anger) that were performed either by ethnic in-group or out-group models. The emotion-specific muscle activities, zygomatic major (ZM) and corrugator supercilii (CS) were recorded simultaneously as the index of facial emotional mimicry. The results first confirm the in-group bias in facial emotional mimicry in the sham condition, as shown in prior studies, though it only occurs in happy mimicry. Moreover, the in-group bias in facial emotional mimicry is modulated by the cortical excitability over the rTPJ, which may be attributed to the accompanied change of overlap of the mental representations of in-group and out-group. This study provides a close look at the neural underpinning of the modulation of facial emotional mimicry by group membership and highlights the role of rTPJ in on-line control of co-activated self and other representations in social cognition.

Right Temporoparietal Junction Plays a Role in the Modulation of Emotional Mimicry by Group Membership

“…Experiment 1 reveals that enhanced cortical excitability over the rTPJ does not improve emotional mimicry. This finding aids the interpretation of our prior research (Peng et al, 2020 ) by ruling out the possibility that the rTPJ regulates facial mimicry toward different emotions. Many previous studies attempting to explore the neural bases for emotional mimicry have demonstrated that both the classical MNS and extended MNS are engaged in emotional mimicry, with the former linked to motor stimulation and the latter linked to the process of affective expressions (Likowski et al, 2012 ; Rymarczyk et al, 2018 , 2019 ).…”

“…As reviewed earlier, although our prior study (Peng et al, 2020 ) revealed alteration in rTPJ activity resulted in change of facial mimicry toward ethnic ingroup and outgroup expressions, it left an open question what the precise role rTPJ exerted in this modulation. The present study aimed to tap this issue by testing the two possible explanations via two experiments.…”

“…All clips were edited to the same 1,000-ms duration, changing from a neutral expression at the beginning to the full-blown emotional expression by the end. The stimuli were validated in our prior work (Peng et al, 2020 ).…”

“…A cover story stated that this study was designed to rate the emotions performed by various models to build a dynamic, happy face database. Here, ethnicity was made salient, as in prior studies (van der Schalk et al, 2011 ; Peng et al, 2020 ), for participants in Experiment 2. In the formal procedure, each trial began with a fixation (300–500 ms) and then with a happy clip (1,000 ms).…”

“…To date, however, why people show this ingroup bias remains an issue. Our recent study (Peng et al, 2020 ) took the first step by showing that the right temporoparietal junction (rTPJ) could modulate ingroup bias in emotional mimicry. Specifically, we recruited a group of college students and randomly assigned them to three transcranial direct current stimulation (tDCS) conditions: anodal, cathodal, and sham.…”