Hippocampal Volume and Circadian Rhythm Characteristics

Abstract

AbstractBackgroundHippocampal atrophy is one of the prominent neurodegenerative features of Alzheimer’s disease and related dementias. Alterations in circadian rhythms and 24‐hour rest activity rhythms can exacerbate cognitive aging and neurodegeneration. The aim of this study was to examine how 24‐hour rest activity rhythms and circadian rhythms are associated with hippocampal volume.MethodWe studied 61 older adults’ data (mean age±SD = 70.0±7.2). T1‐weighted anatomical images from 3T MRI data were collected and processed using the BRAINSTools toolbox. Hippocampal volume was divided by intracranial volume (ICV). Dim light melatonin onset (DLMO) was used to assess circadian timing. Area under the curve (AUC) was calculated based on melatonin levels 6 hours prior to the bedtime. 10‐day actigraphy data assessed 24‐hour rest activity rhythms. Multiple linear regression was used to develop a model for hippocampal volume, controlling for age and sex. Additional covariates (i.e., depressive symptoms, hypertension, coronary artery disease, handedness, and ICV) and moderating effects of age and sex were examined.ResultAcrophase was positively associated with hippocampal volume (b = 0.12, p = .016). Interaction between mesor and age (b = ‐1.22, p = .006) indicated that positive effect of mesor (b = 8.58, p = .007) on hippocampal volume decreased with age. Advanced DLMO time (b = 0.16, p = .005) and greater AUC/10 (b = 0.05, p = .046) were associated with increased hippocampal volume. Amplitude and Pseudo‐F‐Statistics were not associated with hippocampal volume.ConclusionThe findings indicate delayed peak activity time (acrophase), delayed circadian timing (DLMO), and greater mesor and melatonin (AUC) were associated with increased hippocampal volume. The effect of mesor decreased with age. Future studies using larger sample sizes and prospective designs are needed to better understand the relationships.