Anodal tDCS effects over the left dorsolateral prefrontal cortex (L-DLPFC) on the rating of facial expression: evidence for a gender-specific effect.

The accurate recognition of others' facial expressions is a core skill for social interactions. The left Dorsolateral Prefrontal Cortex (L-DLPFC) represents a key node in the network for facial emotion recognition. However, its specific role is still under debate. As such, the aim of the current neuromodulation study was to assess the causal role of the L-DLPFC in humans' rating of facial expressions of emotions and implicit attitudes toward other races. In this sham-controlled single-blind between-subject experiment, we offline administered L-DLPFC transcranial direct current stimulation (tDCS) to 69 healthy participants who were divided into three groups of 23 (each receiving anodal 1 mA tDCS, anodal 2 mA tDCS, or Sham), before completing an "Emotion Rating task and two Implicit Association Tests (IATs). The former required the intensity rating of 192 faces (half black and half white) displaying happiness, sadness, anger, or fear. The IATs were designed to assess participants' automatic associations of positive or negative attributes with racial contents. Results on the Emotion Rating task showed participants' gender-specific effect of tDCS. Specifically, a with only males showing a tendency to underestimate negative emotions was found in Sham, and absent in the tDCS groups. When considering the race of the stimuli, females but not males in Sham exhibited a , that is, the tendency to overestimate negative emotions of other-race faces. Again, the bias disappeared in the tDCS groups. Concerning the IATs, no significant effects emerged. We conclude that the L-DLPFC plays a critical role in humans' rating of facial expressions, and for variability in other-race emotional judgements. These results shed light on the neural bases of the human emotional system and its gender-related differences, and have potential implications for interventional settings.