P049 Actigraphic rest-activity rhythms in older adults ‘at risk’ for dementia: associations with reduced cortical thickness in frontal, temporal and occipital cortices

BACKGROUND: Rest-activity rhythm disturbance is common in older adults ‘at risk’ for dementia. This may be an early marker of underlying disease pathology and risk of future decline. However, our understanding of how rest-activity rhythm relates to brain integrity remains unclear. METHODS: This study used vertex-wise analyses to examine the association between nonparametric actigraphy measures and cortical thickness in older adults ‘at risk’ for dementia. Primary measures of interest were intra-daily variability (IV), relative amplitude (RA), inter-daily stability (IS), and average activity during the least active 5-hour period (L5). RESULTS: 143 older adults ‘at risk’ for cognitive decline were included (mean age=67.41, SD=7.96). Higher IV was associated with lower cortical thickness in the right cuneus (CWP< 0.001), left middle frontal gyrus (CWP< 0.001) and lateral orbital frontal cortex (CWP=0.004). Higher L5 was linked with cortical thinning in the left superior temporal sulcus (CWP=0.004), superior middle temporal cortex (CWP=0.010) and middle temporal gyrus (CWP=0.013), as well as right inferior parietal lobe (CWP< 0.001). Lower IS was associated with cortical thinning in the left (CWP=0.002) and right (CWP< 0.001) superior frontal gyri, left superior temporal gyrus (CWP=0.043) and left post-central gyrus (CWP=0.033). CONCLUSIONS: Markers of circadian rhythmicity are associated with reduced cortical thickness in frontal, temporal and occipital cortices in older adults ‘at risk’ for dementia. Future work is still required to delineate whether brain degeneration leads to altered daily rhythms and/or if circadian misalignment contributes to cognitive decline longitudinally.