The protective effects of executive functions and episodic memory on gait speed decline in aging defined in the context of cognitive reserve

Abstract

Objectives: To evaluate whether levels of cognitive reserve (CR), as measured using the Wechsler Adult Intelligence Scale (WAIS)-III vocabulary test, moderated longitudinal associations between cognitive functions and decline in gait speed in a community-based cohort of older adults without dementia, specifically, whether the protective effect of executive function (EF) and episodic memory against decline in gait speed would be greater in individuals with higher CR.

Design: Longitudinal (median number of repeated annual gait speed measures, 3; maximum number of visits, 7).

Setting: General community.

Participants: Seven hundred thirty-one community-residing individuals aged 70 and older without dementia were followed longitudinally with cognitive and gait evaluations at baseline and at annual visits.

Measurements: Decline in gait speed (cm/s) served as the primary outcome. The Free and Cued Selective Reminding Test (FCSRT) was used to assess episodic memory. The Digit Symbol Substitution Test (DSST) was used to assess attention and EF. The vocabulary test served as a marker for CR.

Results: Linear mixed effects model showed that gait speed declined over the follow-up period (P < .001). The significant three-way interactions of time by DSST by vocabulary (P = .01) and time by FCSRT by vocabulary (P = .02) revealed that levels of CR moderated the longitudinal associations between EF and episodic memory and gait speed decline.

Conclusion: The protective effects of EF and episodic memory against gait speed decline in aging are greater in individuals with higher CR.

Figure 1

Visual depiction of the 3-way interactions of time × Digit Symbol Substitution Test × Vocabulary and time × Free and Cued Selective Reminding Test × Vocabulary on gait speed decline. The Digit Symbol Substitution Test, Free and Cued Selective Reminding Test and Vocabulary were each dichotomized into quartile 4 (best) versus the remaining 3 quartiles. The protective effects of high Digit Symbol Substitution Test scores (4 quartile) vs. lower Digit Symbol Substitution Test scores (quartiles 1-3) are contrasted in low (figure 1panel a) and high (Figure 1 panel b) Vocabulary groups. The protective effects of high Free and Cued Selective Reminding Test scores (4 quartile) vs. lower Free and Cued Selective Reminding Test scores (quartiles 1-3) are contrasted in low (Figure 1 panel c) and high (Figure 1 panel d) Vocabulary groups.