Social interaction: Affective vs. cooperative

The study aims to investigate the neural bases of the observation and comprehension of different types of social interactions, namely "socio-affective" and "collaborative", using functional magnetic resonance imaging. Based on the reports of gender effects in the processing of social and affective stimuli, we also assessed whether cerebral activations when attending these types of social interactions were modulated by the gender of the observer. Participants (13 males and 14 females) were shown images depicting two individuals interacting in order to reach a common goal ("collaborative" condition, such as cooperating to climb a tree) or in an affective way (e.g., to smile at each other) during functional scanning. Observing social interactions, regardless of interaction-type and participants' gender, activated regions involved in the visual analysis of faces and bodies, (fusiform gyrus, extra-striate body area), in visual motion processing (even if implicit in static pictures; area MT/V5), and in the recognition and comprehension of observed actions (superior and inferior parietal lobuli, ventral premotor cortex). This network was more strongly activated by "collaborative" than "socio-affective" pictures, likely reflecting the comprehension of actions-meaning and their agents' intentions. In the opposite comparison, "socio-affective" pictures elicited stronger activity in the right temporal pole and dorsomedial prefrontal cortex, typically associated with "theory-of-mind" processes. Direct gender comparisons did not highlight robust differences when attending generic social interactions (i.e., irrespective of the observed collaborative vs affective picture). Yet, gender differences were observed when separately assessing the two types of images. Observing cooperative vs affective pictures activated more strongly the fronto-parietal mirror system in females and the right nucleus accumbens in males. These results suggest a different coding of the observed collaborative action, leading to simulation in females and reward for the attended cooperation in males. Gender differences while observing affective pictures were less clear-cut, and mainly involved different dorsomedial and ventromedial sectors of prefrontal cortex, which were more strongly activated in females and males, respectively. These results extend the available knowledge on the neural systems underpinning the processing of social information, and provide support to the hypothesis of gender diffences in this domain.