COMPOSITIONS OF 24-HOUR ACTIVITY CYCLE BEHAVIOURS AND BRAIN VOLUME IN PEOPLE WITH MILD COGNITIVE IMPAIRMENT

People with mild cognitive impairment are at greater risk of dementia. Physical activity, sedentary behaviour, and sleep are movement behaviours that constitute the 24-hour activity cycle (24-HAC) and are interactively associated with brain and cognitive health. However, the relationship between compositions of 24-HAC movement behaviours (i.e., time spent in one behaviour relative to the others) and brain volume in people with mild cognitive impairment remains unclear. PURPOSE: Explore whether compositions of 24-HAC movement behaviours predict cortical brain volume and whether cortical volume in 24-HAC-predicted regions are associated with cognitive performance. METHODS: A cross-sectional analysis of 110 community-dwelling adults (55+ years) with mild cognitive impairment. We assessed 24-HAC movement behaviours (5-7 days) using the MotionWatch8©. Compositional data analysis determined 24-HAC movement behaviour compositions with four isometric log ratios coordinates (i.e., one 24-HAC movement behaviour adjusted to the geometric mean of all others). FreeSurfer quantified gray matter volume using T1-weighted magnetic resonance imaging. The ADAS-Cog-Plus assessed cognitive performance. We performed linear regressions, adjusted for age, sex, intracranial volume, and Montreal Cognitive Assessment. Multiple comparisons were adjusted using the false-discovery rate (FDR). RESULTS: Higher compositions of moderate-to-vigorous physical activity predicted greater volume in the inferior temporal gyrus TE2a region (ß = 0.31, FDR-adjusted p = 0.040). Higher compositions of light physical activity predicted lower volume in the inferior temporal gyrus TE2a region (ß = -0.45, FDR-adjusted p = 0.024). Exploratory analyses showed that greater inferior temporal gyrus TE2a region volume predicted better performance in ADAS-Cog-Plus memory tasks of immediate word recall (ß = -0.56, unadjusted p = 0.010) and delayed memory (ß = -0.77, unadjusted p = 0.049). There were no associations of sedentary behaviour or sleep compositions with brain volume (p > 0.05). CONCLUSION: In people with mild cognitive impairment, greater compositions of moderate-to-vigorous physical activity may mitigate atrophy in a signature Alzheimer’s disease region associated with immediate and delayed memory. Jack Brown and Family Alzheimer Research Foundation, Dawn Shaw, Vancouver Coastal Health Research Institute Innovation and Translational Research Awards (F16-01717), Canadian Institutes of Health Research (AWD- 016347; MOP-142206; PJT-148902), and Heart and Stroke Foundation of Canada (G-15-0009019)