Resting Cerebral Blood Flow After Exercise Training in Mild Cognitive Impairment

Abstract

Background: Exercise training has been associated with greater cerebral blood flow (CBF) in cognitively normal older adults (CN). Alterations in CBF, including compensatory perfusion in the prefrontal cortex, may facilitate changes to the brain's neural infrastructure.

Objective: To examine the effects of a 12-week aerobic exercise intervention on resting CBF and cognition in CN and those with mild cognitive impairment (MCI). We hypothesized individuals with MCI (versus CN) would exhibit greater whole brain CBF at baseline and that exercise would mitigate these differences. We also expected CBF changes to parallel cognitive improvements.

Methods: Before and after a 12-week exercise intervention, 18 CN and 17 MCI participants (aged 61-88) underwent aerobic fitness testing, neuropsychological assessment, and an MRI scan. Perfusion-weighted images were collected using a GE 3T MR system. Repeated measures analyses of covariance were used to test within- and between-group differences over time, followed by post-hoc analyses to examine links between CBF changes and cognitive improvement.

Results: At baseline, individuals with MCI (versus CN) exhibited significantly elevated perfusion in the left insula. Twelve weeks of aerobic exercise reversed this discrepancy. Additionally, exercise improved working memory (measured by the Rey Auditory Verbal Learning Test) and verbal fluency (measured by the Controlled Oral Word Association Test) and differentially altered CBF depending on cognitive status. Among those with MCI, decreased CBF in the left insula and anterior cingulate cortex was associated with improved verbal fluency.

Conclusions: Exercise training alters CBF and improves cognitive performance in older adults with and without cognitive impairment. Future studies must evaluate the mediating effects of CBF on the association between exercise training and cognition.

Keywords: Aging; cerebral blood flow; exercise; magnetic resonance imaging; mild cognitive impairment; neuroimaging.

Figure 1.

The box encompassing the brain maps above represents the field of view (FOV) that was used for image acquisition during this study. The green colored area illustrates the standardized gray matter mask within which the voxel-wise analysis was restricted. The brain mask was generated using AFNI’s 3dMerge program and included only those voxels in which ≥ 95% of the study sample had data. Data from voxels not meeting this threshold were excluded from the group analyses.

Figure 2.

Bold p-value indicates a significant between-group difference, family wise error corrected p < 0.05. (A) Brain maps and corresponding strip plots showing significant difference at baseline (CN < MCI) in the left insula (the location of peak difference). (B) Demonstrates the comparison after the exercise intervention (CN = MCI). The baseline difference (shown in red) spans several brain regions including the left insula (BA 46), putamen (BA 25), inferior frontal gyrus (BA 47), and medial frontal gyrus (BA 10). There was no significant between-group difference in the left insula, or any other brain region, after the exercise intervention.

Figure 3.

Bold p-values indicate significant within-group changes over time, family-wise error corrected p < 0.05. (A) Brain map and corresponding strip plot show significant changes over time for CN. Red area indicates significantly increased CBF in the right anterior cingulate cortex (location of peak change), but also spans the left/right anterior cingulate cortices and the left/right superior medial gyri (BA 10). (B) Shows significant changes over time for MCI, with the blue area indicating decreased CBF in the left anterior cingulate cortex (location of peak change). (C) Also shows significant changes over time for MCI, with the blue area indicating decreased CBF in the right inferior frontal gyrus (location of peak change). Significant CBF changes in those with MCI span several brain regions including the left/right anterior cingulate cortex (BA 24), left/right middle cingulate cortex (BA 32), right inferior frontal gyrus (BA 47), right insula (BA 46), and right putamen (BA 25).

Figure 4.

After adjustment for age and education, scatterplots depict the partial correlations between residualized change in COWAT performance and residualized change in CBF among individuals diagnosed with MCI. Improved COWAT performance was associated with (A) decreased left insula CBF and (B) decreased left ACC CBF among individuals with MCI. No such associations were found among CN individuals.