Courtesy of Naif Majrashi and Dr Gordon Waiter, this image shows seasonal changes in hippocampal subfield volume measurements from brain MRI in a sample of more than 10,000 participants in the UK Biobank study. The study has acquired data year-round from a relatively healthy sample of adults in middle and older age, including brain MRI data collection at a single scanning center. Hours of daylight at the UK Biobank scanning centre range from 7.49 hr in winter to 17.01 hr in summer; this image shows results of an investigation into whether seasonal changes in day length are associated with not only total hippocampal volume but also with hippocampal subfield volumes in humans (as has been reported in studies of other animals). Volumetric analysis found seasonal changes amounting to approximately 15 mm3 per hour of daylight, from mid‐winter to mid‐summer, and additionally revealed sex differences in the rate of change.

FreeSurfer software was used to perform hippocampal subfield segmentation, as shown in sagittal (top) and axial (bottom) brain MRI images (a). A coronal section schematic illustrates the anatomy of analysed hippocampal subfields: DG; dentate gyrus and CA; cornu ammonis (b). Rate of change in left and right hippocampal subfield volumes per unit hour (mm3/hr) is presented for females and males (c). Positive correlations were found between photoperiod (the number of hours between sunrise and sunset on the day the MRI scan was performed) and total hippocampal volume, and all subfield volumes, across participants as well as in each sex individually, with females showing greater seasonal variation in a majority of left subfield volumes compared with males.


The image is taken from a recent study published in Brain and Behavior:

Majrashi NA, Ahearn TS, Williams JHG, Waiter GD. Sex differences in the association of photoperiod with hippocampal subfield volumes in older adults: A cross‐sectional study in the UK Biobank cohort. Brain Behav 2020; e01593.