Dose-dependent association of accelerometer-measured physical activity and sedentary time with brain perfusion in aging

Abstract

Introduction: Age-related decreases in cerebral blood flow (CBF) may lead to cognitive decline, while physical activity (PA) can maintain CBF and cognition in aging. The intensity of PA needed to affect CBF in aging, and the independent effects of sedentary time on CBF are currently unknown. Moreover, research conducted in free-living environments with objective measures of PA (e.g., accelerometry) is lacking.

Methods: This cross-sectional study used accelerometry to objectively measure sedentary time, all light PA [AllLightPA], moderate-to-vigorous PA [MVPA], and total activity counts [TAC] in 52 cognitively healthy older adults. Robust linear regressions investigated the association of CBF (using arterial spin labeling magnetic resonance imaging) in frontal and medial temporal regions, with each PA intensity and sedentary time.

Results: Greater sedentary time was significantly associated with lower CBF in lateral and medial frontal regions after adjusting for MVPA, while higher AllLightPA (adjusted for MVPA), MVPA (adjusted for AllLightPA), and TAC were associated with greater CBF in lateral and medial frontal regions.

Discussion: Lighter activities, as well as MVPA, are beneficial to CBF in brain regions typically affected by the aging process and malleable to exercise interventions (i.e., the frontal lobes), whereas sedentary time is an independent risk factor for neurovascular dysregulation in normal aging.

Keywords: Accelerometry; Cerebral blood flow; Cognition; Dose-response; Physical activity; Sedentary time.

Figure 1:. Regions of Interest (ROIs) selected for search region regression models

Figure 1 Notes: Frontal (yellow) and Hippocampal/Parahippocampal (red) Regions of Interest (ROIs) used in the search region analyses. The Frontal ROI was derived from the MNI Atlas available in FSL. The Hippocampal/Parahippocampal ROI was derived from the Harvard-Oxford Subcortical and Cortical Atlases respectively.

Figure 2:. ROI analyses: areas within the frontal ROI with significant associations of CBF and accelerometer measures.

Figure 2 Notes: Locations within the frontal cortex region of interest (ROI) where there were significant associations of cerebral blood flow (CBF) with accelerometer measures. Cluster numbers (c1, c2, c3, etc) in this figure correspond to those in Table 3. Refer to Table 3 for cluster locations and coordinates. Negative X coordinates correspond to the left hemisphere, while positive X coordinates correspond to the right hemisphere in MNI space (3 × 3 × 3 mm).

Figure 3.. Scatterplots of accelerometer measures with CBF extracted from significant clusters in the frontal lobe ROI.

Figure 3 Notes: Scatterplots depict the direction of associations between the unstandardized residuals of cerebral blood flow (CBF) on the Y-axis (adjusted for covariates) and the different accelerometer measures on the X-axis. CBF is measured in mL/100g of tissue/minute, but these plots represent the unstandardized residuals (explaining why values in the Y axis range from positive to negative). For total activity counts (TAC) and sedentary time, the mean CBF was averaged across all significant clusters for display purposes (the direction of associations was consistent within each individual cluster). AllLight PA= All light physical activity; MVPA= Moderate to vigorous physical activity; R= Right; L=Left; IFG=Inferior frontal gyrus; MFG=Middle frontal gyrus; CBF=Cerebral blood flow; ROI=Region of interest.