Neural signature of everyday function in older adults at-risk of cognitive impairment

Abstract

Assessment of everyday activities are central to the diagnosis of pre-dementia and dementia. Yet, little is known about the brain substrates and processes that contribute to everyday functional impairment, particularly during early stages of cognitive decline. We investigated everyday function using a complex gait task in normal older adults stratified by risk of cognitive impairment. We applied a novel EEG approach, which combines electroencephalographic with 3D-body tracking technology to measure brain-gait dynamics with millisecond precision while participants are in motion. Twenty-six participants (mean age = 74.9 years) with cognitive and everyday functional profiles within the normal range for their age and sex were ranked for risk of cognitive impairment. We used the Montreal Cognitive Assessment battery, a global index of cognition with a range from 0 to 30, to classify individuals as being at higher (22-26) and lower risk (27+). Individuals walking on a treadmill were exposed to visual perturbation designed to destabilize gait. Assuming that brain changes precede behavioral decline, we predicted that older adults increase step width to gain stability, yet the underlying neural signatures would be different for lower versus higher risk individuals. When pooling across risk groups, we found that step width increased and fronto-parietal activation shifted from transient, during swing phases, to sustained across the gait cycle during visually perturbed input. As predicted, step width increased in both groups but underlying neural signatures were different. Fronto-medial theta (3-7Hz) power of gait-related brain oscillations were increased in higher risk individuals during both perturbed and unperturbed inputs. On the other hand, left central gyri beta (13-28Hz) power was decreased in lower risk individuals, specifically during visually perturbed input. Finally, relating MoCA scores to spectral power pooled across fronto-parietal regions, we found associations between increased theta power and worse MoCA scores and between decreased beta power and better MoCA scores.Able-bodied older adults at-risk of cognitive impairment are characterized by unique neural signatures of mobility. Stronger reliance on frontomedial theta activation in at-risk individuals may reflect higher-order compensatory responses for deterioration of basic sensorimotor processes. Region and spectral-specific signatures of mobility may provide brain targets for early intervention against everyday functional decline.