Rest-activity rhythm fragmentation and synchronization are linked with reduced cortical thickness in older adults "at...

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.

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

When controlling for age, sex, and body mass index (BMI), lower IV was associated with greater cortical thickness in the right cuneus (cluster-wise p-values [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.

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. Further studies could focus on determining the prognostic utility of such markers longitudinally.