The Associations Between Cardiorespiratory Fitness, Hippocampal Health, And Cognition In Mild Cognitive Impairment

Abstract

Mild cognitive impairment (MCI), a prodromal stage of Alzheimer’s disease, has negative effects on cognition and is associated with structural changes in the brain, particularly the hippocampus. We utilized magnetic resonance elastography (MRE), an imaging technique that estimates brain mechanical properties, to quantify the integrity of the underlying tissue microstructure. MRE is an emerging method for evaluating hippocampal health and its relation to cognition. We used MRE to assess the relationship between aerobic fitness and hippocampal integrity in MCI and aging, as fitness is a modifiable lifestyle factor. Establishing these links can help identify those at risk of cognitive impairment and establish interventions. PURPOSE: To demonstrate the value of MRE measures of hippocampal health to assess the relationship between aerobic fitness, cognition, and MRE in MCI. METHODS: We recruited 47 healthy older adults (69 ± 6 yrs) and 13 with amnestic MCI (72 ± 9 yrs). Participants had an MRI, fitness and cognitive testing to collect hippocampal stiffness and damping ratio, reflecting the resistance of tissue, relative VO2,max, and a composite cognitive score. RESULTS: Older adults had significantly higher stiffness (p < .01) and lower damping ratio (p = .001). Stiffness significantly mediated the relationship between diagnosis and cognition (Estimated indirect effect, ACME (95% CI) = .04 (-.004, -.009)). VO2 was differentially associated with MRE measures in MCI compared healthy older adults. A significant diagnosis x fitness interaction effect was observed (Stiffness: β = .012, SE = .006, p = .041; Damping ratio: β = -.001, SE = .001, p = .041), with a stronger relationship between VO2 and MRE measures in the MCI group (Stiffness: p = .029, 95% CI = .075, .881; Damping ratio: p = .243, 95% CI = -.74, .33) compared to in the healthy older group (Stiffness: p = .191, 95% CI = -1.01, .49; Damping ratio: p = .764, 95% CI = -.36, .27). Only stiffness was associated with fitness in MCI participants. CONCLUSIONS: These preliminary findings suggest the utility of MRE in studying the mechanism of disease, with stiffness mediating the relationship between groups and cognition. Fitness is related to MRE outcomes in MCI, specifically stiffness, suggesting that higher aerobic fitness may be even more beneficial for those with MCI.