Abstract
Objective: Although previous studies postulated that physical and cognitive decline codeveloped in preclinical dementia, the interconnected relationship among subjective cognitive complaints (SCCs), objective cognitive performance, and physical activity remained hazy. We investigated the mediating roles of physical activity between subjective and objective cognition. Diffusion tensor imaging (DTI) was utilized to test our hypothesis that brain white matter microstructural changes underlie the physical-cognitive decline in subjective cognitive decline (SCD).Methods: We enrolled cognitively normal older adults aged > 50 years in the Community Medicine Research Center of Keelung Chang Gung Memorial Hospital during 2017–2020. Regression models analyzed mediation effects of physical activity between subjective and objective cognition. The self-reported AD8 questionnaire assessed SCCs. The SCD group, defined by AD8 score ≥ 2, further underwent diffusion MRI scans. Those who agreed to record actigraphy also wore the SOMNOwatch™ for 72 h. Spearman's correlation coefficients evaluated the associations of diffusion indices with physical activity and cognitive performance.Results: In 95 cognitively normal older adults, the AD8 score and the Montreal Cognitive Assessment (MoCA) score were mediated partially by the metabolic equivalent of the International Physical Activity Questionnaire-Short Form (IPAQ-SF MET) and fully by the sarcopenia score SARC-F. That is, the relation between SCCs and poorer cognitive performance was mediated by physical inactivity. The DTI analysis of 31 SCD participants found that the MoCA score correlated with mean diffusivity at bilateral inferior cerebellar peduncles and the pyramids segment of right corticospinal tract [p < 0.05, false discovery rate (FDR) corrected]. The IPAQ-SF MET was associated with fractional anisotropy (FA) at the right posterior corona radiata (PCR) (p < 0.05, FDR corrected). In 15 SCD participants who completed actigraphy recording, the patterns of physical activity in terms of intradaily variability and interdaily stability highly correlated with FA of bilateral PCR and left superior corona radiata (p < 0.05, FDR corrected).Conclusions: This study addressed the role of physical activity in preclinical dementia. Physical inactivity mediated the relation between higher SCCs and poorer cognitive performance. The degeneration of specific white matter tracts underlay the co-development process of physical-cognitive decline in SCD.
Highlights
IntroductionSubjective cognitive decline (SCD) is defined by presence of subjective cognitive complaints (SCCs) and absence of cognitive impairment or neuropsychiatric deficits
According to the National Institute on Aging and the Alzheimer’s Association guideline, subjective awareness of subtle cognitive decline occurs at the preclinical stage of Alzheimer’s disease (Sperling et al, 2011)
Our results further suggested that CST influences cognitive performance partly through physical activity in preclinical dementia
Summary
Subjective cognitive decline (SCD) is defined by presence of subjective cognitive complaints (SCCs) and absence of cognitive impairment or neuropsychiatric deficits. In SCD, compensatory mechanisms preserve the cognitive performance, and the severe cognitive decline has not yet begun (Jessen et al, 2014). SCCs identified the risk of cognitive decline in older adults, that is, people with memory complaints had a 6.67% annual conversion rate to mild cognitive impairment (MCI) and a relative risk of dementia of 2.07, compared with those without SCCs (Mitchell et al, 2014). A community study of non-demented older adults found the relationship between impaired cognitive performance and physical frailty (Wu et al, 2015). Physical frailty has been reported positively associated with the decline of both subjective and objective cognition in older non-demented women (Gifford et al, 2019). An interconnected triangle relationship seemed to emerge among physical activity, subjective cognition, and objective cognition, the causal relationship among these three aspects remained hazy
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