Abstract
IntroductionEven though seasonal and sex‐dependent changes in hippocampal and subfield volumes are well known in animals, little is known about changes in humans. We hypothesized that changes in photoperiod would predict changes in hippocampal subfield volumes and that this association would be different between females and males.MethodsA total of 10,033 participants ranging in age from 45 to 79 years were scanned by MRI in a single location as part of the UK Biobank project. Hippocampal subfield volumes were obtained using automated processing and segmentation algorithms using the developmental version of the FreeSurfer v 6.0. Photoperiod was defined as the number of hours between sunrise and sunset on the day of scan.ResultsPhotoperiod correlated positively with 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. ANCOVAs revealed significant differences in rate of change in only left subiculum, CA‐4, and GC‐ML‐DG between females and males. PLS showed highest loadings of hippocampal subfields in both females and males in GC‐ML‐DG, CA1, CA4, subiculum, and CA3 for left hemisphere and CA1, GC‐ML‐DG, CA4; subiculum and CA3 for right hemisphere in females; GC‐ML‐DG, CA1, subiculum, CA4 and CA3 for left hemisphere; CA1, GC‐ML‐DG, subiculum, CA4 and CA3 for right hemisphere in males.ConclusionThe influence of day length on hippocampal volume has implications for modeling age‐related decline in memory in older adults, and sex differences suggest an important role for hormones in these effects.
Highlights
Even though seasonal and sex-dependent changes in hippocampal and subfield volumes are well known in animals, little is known about changes in humans
White-footed mice Peromyscus leucopus exhibit smaller hippocampal volume when exposed to shorter photoperiods (8-hr day length) compared with those exposed to longer photoperiods (16-hr day length), (Sherry & Hoshooley, 2010; Yaskin, 2011) and hippocampal mass is significantly decreased in bank voles during the winter season compared with the autumn or summer seasons (Yaskin, 2011)
Reduced hippocampal mass in bank voles Clethrionomys glareolus in winter could be due to smaller dentate gyrus (DG), CA3, and CA4 hippocampal subfields compared with the autumn samples (Yaskin, 2013)
Summary
Even though seasonal and sex-dependent changes in hippocampal and subfield volumes are well known in animals, little is known about changes in humans. We hypothesized that changes in photoperiod would predict changes in hippocampal subfield volumes and that this association would be different between females and males. Results: Photoperiod correlated positively with 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 volume of the hippocampus may be associated with photoperiod and be smaller in winter compared with summer (Clayton, Reboreda, & Kacelnik, 1997; Pyter, Reader, & Nelson, 2005; Workman, Manny, Walton, & Nelson, 2011; Yaskin, 2011). Reduced hippocampal mass in bank voles Clethrionomys glareolus in winter could be due to smaller dentate gyrus (DG), CA3, and CA4 hippocampal subfields compared with the autumn samples (Yaskin, 2013)
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