Mood, season and light within the amygdala

The brain mechanisms through which changes in seasonality and light exposure modulate affective state may involve different nuclei of the amygdala. We aimed to test this hypothesis using 7 Tesla functional magnetic resonance imaging in 29 healthy young adults. We first considered the seasonal changes in activity, that are related to the slow change in photoperiod. We find that the activity of medial and superior nuclei of the amygdala is related to season and affective state. We further assessed how alternating short exposures to light of different illuminance acutely affected the regional activity of the amygdala. We show that the same medial and superior nuclei showed a linear reduction of activity when exposed to increasing light illuminance, specifically when processing emotional stimulations. Importantly also, the impact of light on part of these nuclei varied with season and affective state. These findings provide new evidence that humans show seasonality and that for affective states it involved parts of the amygdala. The results bring novel insights into the mechanisms that underlie the long-term and acute impact of light on the affective system and that may contribute to the benefits of light therapy in the treatment of mood disorders.