Rest activity rhythm fragmentation and synchronisation are linked with reduced cortical thickness in older adults 'at risk' for dementia.

Abstract

Study objectives: While alterations in rest-activity rhythms are common in older adults 'at risk' for dementia, it is unclear how rest-activity rhythms relate to underlying brain integrity.

Methods: Older adults aged > 50 years (n=143, mean age=67) with subjective and/or objective cognitive impairment underwent MRI scanning and 14-days of actigraphy. The following non-parametric measures were computed: intra-daily variability (IV), inter-daily stability (IS), relative amplitude (RA), and average activity during the least active 5-hour period (L5). A vertex-wise analysis correcting for age, sex and clinical variables examined the association between nonparametric actigraphy measures and cortical thickness.

Results: When controlling for age, sex, and body mass index (BMI), lower IV was associated with greater cortical thickness in the right cuneus (CWP< 0.001), left middle frontal gyrus (CWP< 0.001) and lateral orbital frontal cortex (CWP= 0.004). When controlling for age, sex, medical burden (CIRS-G), BMI and antidepressant use, lower IS was associated with lower cortical thickness in the left (CWP= 0.002) and right superior frontal gyrus (CWP< 0.001), left superior temporal gyrus (CWP= 0.043) and left post-central gyrus (CWP= 0.033). There were no significant associations between RA or L5 and cortical thickness.

Conclusions: In older adults 'at risk' for dementia, variability and stability of rest-activity rhythms were associated with reduced cortical thickness in frontal, temporal, parietal and occipital regions. Studies are now required to determine the prognostic utility of such markers longitudinally.