Neural Correlates of postural instability in older adults

Postural instability, common in older age, has been associated with worse cognitive function; however, the neurobiological basis for these associations are not known. We propose postural instability may be a biomarker of lower cognitive function. We aimed to quantify the neural correlates of postural instability in community dwelling older adults with a range of cognitive function. Postural instability was recorded using conventional [postural sway antero-posterior (AP) and medio-lateral (ML) eyes open/closed/foam surface conditions] and a novel ML visual tracking task (MLVT) at 0.125, 0.25, 0.50 and 0.75 Hz frequencies in 179 participants [ (82 years old, Female (54%), White (71.1%) ] of the Health Aging and Body Composition Study. An extensive cognitive battery was obtained, and cognitive status was adjudicated as cognitively normal (CN), mild cognitive impairment (MCI) or dementia using Alzheimer’s Disease Research Center protocols. White matter hyperintensities (WMH), grey matter volume (GMV) and mean diffusivity of total and brain regions of interest (hippocampus, precuneus, anterior, middle and posterior cingulum for both hemispheres) were acquired using 3T MRI with diffusion tensor. ANOVA and multinomial linear regression were used for statistical analyses, adjusting for variables potentially influencing postural control and/or cognition: brain atrophy, race, body mass index and education. Postural instability was higher in MCI and dementia groups compared to CN for all MLVT frequencies. For MLVT=0.25, the odds of postural instability were 1.72 (95% CI 1.25, 2.38) times higher in dementia and 1.16 (95% CI 0.87, 1.55) times higher in MCI groups compared to CN. Greater postural instability was also associated with lower total brain GMV in MCI (β=-0.01, p=0.04) and Dementia (β=-0.02, p=0.006), but not in CN; Greater postural instability was associated with lower regional GMV of bilateral hippocampus, precuneus and cingulum in those with Dementia only. The public health relevance of these findings is significant; our results may help understand the role of postural instability as an early indicator of Dementia. Hippocampus and precuneus could be a shared resource for cognition and postural control