Frailty Is Associated With Cognitive Decline Independent of Cerebral Small Vessel Disease and Brain Atrophy.

BACKGROUND: To examine the effect of frailty on cognitive decline independent of cerebral small vessel disease (cSVD) and brain atrophy, and whether associations between neuropathology and cognition differed depending on frailty status. METHODS: The Tasmanian Study of Cognition and Gait was a population-based longitudinal cohort study with data collected at 3 phases from 2005 to 2012. Participants aged 60-85 were randomly selected from the electoral roll. Various data were used to operationalize a 36-item frailty index (FI) at baseline. Brain MRI was undertaken to obtain baseline measures of neuropathology. A neuropsychological battery was used to assess cognition at each time point. Generalized linear mixed models were used to examine the effect of frailty and MRI measures on cognition over time. The associations between MRI measures and cognition were explored after stratifying the sample by baseline frailty status. All analyses were adjusted for age, sex, and education. RESULTS: A total of 385 participants were included at baseline. The mean age was 72.5 years (standard deviation [SD] 7.0), 44% were female (n = 171). In fully adjusted linear mixed models, frailty (FI × time ß -0.001, 95% confidence interval [CI] -0.003, -0.001, p = .03) was associated with decline in global cognition, independent of brain atrophy, and cSVD. The association between cSVD and global cognition was significant only in those with low levels of frailty (p = .03). CONCLUSION: These findings suggest that frailty is an important factor in early cognitive dysfunction, and measuring frailty may prove useful to help identify future risk of cognitive decline.

The association between simple reaction time variability and gait variability: The Tasmanian Study of Cognition and Gait.

INTRODUCTION: Greater double support time (DST) variability is associated with falls and memory decline. The underlying neurophysiological mechanisms of DST variability are poorly understood. Simple reaction time (SRT) variability, a measure of attention-processing speed is associated with falls and dementia and, may underlie greater DST variability. The aims of this study were to examine the association between SRT and DST variability and if SRT variability mediates the associations between poorer cognition/brain structure and DST variability. METHODS: Participants (n = 408) were community-dwelling older people without dementia (mean age 72.0 ± 7.0). DST variability was the standard deviation (SD) of DST, assessed with a walkway and averaged across steps of 6 walks. SRT variability was the SD of a button pressing task in response to a visual stimulus. Executive function and processing speed were assessed with neuropsychological tests. Magnetic Resonance Imaging was used to obtain cortical thickness (total and in frontal regions) and cerebral small vessel disease (cSVD). Multivariable linear regression models were used to examine the association between SRT and DST variability and if SRT variability mediated any associations of cognition/brain structure with DST variability. RESULTS: Greater SRT variability was associated with greater DST variability (p = 0.002). SRT variability partially mediated the association between poorer executive function and greater DST variability. Smaller mean thickness in orbitofrontal regions and greater cSVD burden were only associated with DST variability (p < 0.05), not with SRT variability (p > 0.05). CONCLUSIONS: Greater SRT variability, which may occur due to inefficient executive functioning, could be an underlying neurophysiological mechanism of greater DST variability.