Tracing Diurnal Differences in Brain Anatomy with Voxel-Based Morphometry – Associations with Sleep Characteristics

Abstract

In recent decades magnetic resonance imaging (MRI) has established itself as the golden standard for studying human brain structure in health and disease. As a result, it has become increasingly more important to identify factors that may influence study outcomes and contribute to misleading conclusions. With the regional time-of-day (TOD) differences in structural brain metrics utterly neglected and several studies reporting inconsistent TOD changes on the global brain level, this work set out to investigate this phenomenon with voxel-based (VBM) and surface-based morphometry (SBM) using the largest longitudinal dataset to date (N = 77). VBM revealed ubiquitous and often bilaterally symmetric differences in local grey and white matter volume across multiple cortical and subcortical brain regions. The impact of TOD on regional SBM indices was less pronounced than for VBM, and no significant effects were observed for the global volume- and surface-based anatomical metrics. Our findings likely reflect a combination of experience- and circadian-related processes, with the former possibly linked to memory formation. By showing that TOD has a prevalent effect on local anatomical brain metrics, our study underlines the need for this factor to be strictly controlled at the stage of experimental planning and data analysis.

Circadian rhythms tied to changes in brain morphology in a densely-sampled male

“…Shorter photoperiods have been associated with smaller total hippocampal volumes (Miller et al, 2015) and smaller brainstem volumes (Majrashi et al, 2020). In contrast, (Zareba et al, 2024) reported an increase in GMV in the amygdala and hippocampus from morning to evening. The present study, which tracks brain and hormone dynamics at a high temporal resolution, suggests an overall decline in cortical and subcortical GMV from morning to evening-a pattern that mirrors the diurnal decrease in steroid hormones.…”

“…Human MRI studies have begun to characterize the role of circadian rhythms in modulating brain structure and function. There are reports of diurnal differences in functional connectivity (Farahani et al, 2021;Orban et al, 2020), cerebral blood flow (Elvsåshagen et al, 2019), water diffusivity (Thomas et al, 2018;Tuura et al, 2021), and brain volume (Karch et al, 2019;Trefler et al, 2016;Zareba et al, 2023Zareba et al, , 2024. However, the association between circadian changes in hormone production and rhythmic changes in the brain is unclear.…”