The role of amygdala reactivity in affective fluctuations across social contexts.

The amygdala plays a critical role in socio-emotional processing, serving not only as a key neural substrate for shaping emotional experiences and social behavior, but also as a trait-like individual risk factor that confers heightened vulnerability to emotional disorders, including anxiety and depression. While prior research has primarily examined the link between heightened amygdala reactivity and negative affect (NA), much less is known about its relationship with positive affect (PA), particularly across different social contexts. In this study, we focused on how these associations vary based on the level of social intimacy and distinct facets of affect (e.g., high vs. low-arousal PA). Using a combined fMRI and ecological momentary assessment (EMA) approach, we examined how individual differences in amygdala reactivity relate to momentary emotional experiences across diverse social contexts in daily life. As expected, interactions with close companions had a robust mood-enhancing effect. Notably, individual differences in amygdala reactivity moderated the association between social context and high-arousal PA, such that individuals with heightened amygdala reactivity reported lower levels of high-arousal PA when alone, compared to when they were with close others. These findings highlight the specific social contexts and affective states most relevant to individual differences in amygdala reactivity, offering novel insights into the dynamic interplay between brain function, emotional experiences, and social contexts.