Date of Award

8-9-2014

Document Type

Open Access Dissertation

Department

Exercise Science

First Advisor

Sara Wilcox

Second Advisor

Roger Newman-Norlund

Abstract

Cognitive reserve theory suggests that physical activity may protect individuals from cognitive decline. At the brain level, greater cognitive reserve may manifest as greater neural network efficiency. Our purpose was to investigate 1) whether participation in a 16-week walking program increased brain efficiency, and 2) whether increased brain efficiency correlated with change in fitness and task performance. Our secondary purpose was to investigate whether exercise training improved performance on a battery of cognitive tasks, particularly executive functioning performance. Seventeen healthy but sedentary women aged 60-75 years participated in a supervised walking program; eighteen women served as a non-randomized control group. Twelve women in the intervention group underwent fMRI scanning at baseline and post exercise training.

During fMRI scanning, participants (mean age 63 years) completed a working memory task (Sternberg delayed-match-to-sample letter task). Participants showed a greater capacity to recruit task-related brain regions after exercise training (indicated as greater BOLD signal). These regions included left inferior frontal gyrus, left cuneus, right rolandic operculum, left middle temporal gyrus, left postcentral gyrus, left superior med frontal, left superior frontal gyrus, right caudate, right inferior temporal gyrus (ps < 0.001). No task-related brain regions were utilized more efficiently after exercise training (ps > 0.001). These findings suggest that exercise-induced cognitive reserve may present as a greater ability to recruit neural resources, rather than greater brain efficiency, in this sample. As there were no significant correlations between changes in task-related brain activation and changes in performance (reaction time slope) with exercise training (r values < 0.49), these findings should be interpreted with caution.

A slightly larger sample of intervention participants (n=17; mean age 64 years) completed a battery of cognitive tasks (CANTAB®) before beginning and after completing exercise training; a matched control group of participants (n=18; mean age 66) completed the battery on dates approximately 16 weeks apart. Based on ANOVA analyses utilizing residualized change scores, there were no significant differences between the groups on any cognitive performance measures (ps > 0.24). Due to the small sample size, we also calculated effect sizes. Effects of the exercise intervention were small for the total trial and total error outcomes on the paired associate learning task (d=0.20 and d=0.39, respectively), as well as for the spatial span task (d=0.38). For the control group, effect sizes were small for the verbal free recall task (d=0.23), medium for the rapid visual processing (d=0.62) and paired associate learning task (d=0.71 and d=0.52 for the total trial and total error outcomes, respectively), and large for the spatial span task (d=1.02). These findings are unexpected, but plausible explanations have been realized and are discussed.

Rights

© 2014, Katie Marie Becofsky

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