Photoperiod Is Associated With Hippocampal Volume in a Large Community Sample

ABSTRACT: Although animal research has demonstrated seasonal changes in hippocampal volume, reflecting seasonal neuroplasticity, seasonal differences in human hippocampal volume have yet to be documented. Hippocampal volume has also been linked to depressed mood, a seasonally varying phenotype. Therefore, we hypothesized that seasonal differences in day-length (i.e., photoperiod) would predict dif-ferences in hippocampal volume, and that this association would be linked to low mood. Healthy participants aged 30–54 (M5 43; SD5 7.32) from the University of Pittsburgh Adult Health and Behavior II project (n5404; 53 % female) were scanned in a 3T MRI scanner. Hippocampal volumes were determined using an automated segmenta-tion algorithm using FreeSurfer. A mediation model tested whether hip-pocampal volume mediated the relationship between photoperiod and mood. Secondary analyses included seasonally fluctuating variables (i.e., sleep and physical activity) which have been shown to influence hippo-campal volume. Shorter photoperiods were significantly associated with higher BDI scores (R250.01, b520.12, P5 0.02) and smaller hippo-campal volumes (R250.40, b5 0.08, P5 0.04). However, due to the lack of an association between hippocampal volume and Beck Depres-sion Inventory scores in the current sample, the mediation hypothesis was not supported. This study is the first to demonstrate an association between season and hippocampal volume. These data offer preliminary evidence that human hippocampal plasticity could be associated with photoperiod and indicates a need for longitudinal studies. VC 2014 Wile