The superior temporal gyrus (STG) has been found to play a crucial role in the recognition of actions and facial expressions and may, therefore, be critical for the processing of humorous information. Here we investigated whether tDCS application to the STG would modulate the ability to recognize and appreciate the comic element in serious and comedic situations of misfortune. To this aim, the effects of different types of tDCS stimulation on the STG were analyzed during a task in which the participants were instructed to categorize various misfortunate situations as "comic" or "not comic". Participants underwent three different tDCS conditions: Anodal-right/Cathodal-left; Cathodal-right/Anodal-left; Sham. Images depicting people involved in accidents were grouped into three categories based on the facial expression of the victim: angry or painful (Affective); bewildered and funny (Comic); and images that did not contain the victim's face (No Face). An improvement in mean reaction times in response to both the Comic and No Face stimuli was observed following Anodal-left/Cathodal-right stimulation when compared to sham stimulation. This suggests that this stimulation type reduced the reaction times to socio-emotional complex scenes, regardless of facial expression. The Anodal-right/Cathodal-left stimulation reduced the mean reaction times for Comic stimuli only, suggesting that specifically the right STG may be involved in facial expression recognition and in the appreciation of the comic element in misfortunate situations. These results suggest a functional hemispheric asymmetry in STG response to social stimuli: the left STG might have a role in a general comprehension of social complex situations, while the right STG may be involved in the ability to recognize and integrate specific emotional aspects in a complex scene.
Keywords: Emotion; Facial expression; Humor; Superior temporal gyrus; Transcranial direct current stimulation.