Amygdala and subregion volume are associated with photoperiod and seasonal depressive symptoms: A cross sectional study in the UK Biobank cohort

Although seasonal changes in amygdala volume have been demonstrated in animals, seasonal differences in human amygdala subregion volumes have yet to be investigated. Amygdala volume has also been linked to depressed mood. Therefore, we hypothesized that differences in photoperiod would predict differences in amygdala or subregion volumes, and that this association would be linked to depressed mood. 10,033 participants ranging in age from 45 to
79 years, were scanned by MRI in a single location. Amygdala subregion volumes were obtained using automated processing and segmentation algorithms. A mediation analysis tested whether amygdala volume mediated the relationship between photoperiod and mood. Photoperiod was positively associated with total amygdala volume (p <.001). Multivariate (GLM) analyses revealed significant effects of photoperiod across all amygdala subregion volumes for both hemispheres (p <.001). Post-hoc univariate regression analyses revealed
significant associations of photoperiod with each amygdala subregion volume (p <.001). PLS showed highest loadings of amygdala subregions in lateral nucleus, ABN, basal nucleus, CAT, PLN, AAA, central nucleus, cortical nucleus, and medial nucleus for left hemisphere, and ABN, lateral nucleus, CAT, PLN, cortical nucleus, AAA, central nucleus, and medial nucleus for right hemisphere. There were no significant associations between photoperiod and mood nor between mood scores and amygdala volumes, and due to the lack of these associations the
mediation hypothesis was not supported. This study is the first to demonstrate an association between photoperiod and amygdala volume. These findings add to the evidence supporting the role of photoperiod on brain structural plasticity.