The effect of mild cognitive impairment on reactive stepping responses and motor adaptation to trip perturbations - This study examines differences in reactive stepping responses between older adults with mild cognitive impairment and cognitively intact older adults when exposed to novel and repeated gait-trip perturbations. Falls occur in >30% of older adults each year, most often due to trips, and lead to ~2.8 million hospital admissions, 32,000 deaths, and $50 billion in medical costs. Fall incidence is doubled in older adults with mild cognitive impairment (OAwMCI), which is a prodromal stage of dementia that affects about 17% of the aging population. Substantial evidence indicates that OAwMCI have impaired volitional balance control and gait compared to cognitively intact older adults (CIOA); however, the underlying mechanisms that explain why OAwMCI have a greater predisposition to falls are yet to be investigated. The main causative factors of falling have been identified as deficits in reactive balance control, including reduced center of mass (COM) stability and insufficient vertical limb support post-perturbation, which could be associated with impaired neuromuscular coordination (reduced muscle synergies). Further, evidence from mobile neuroimaging techniques such as electroencephalography (EEG) suggest the role of the cortex in generating a reactive stepping response, as indicated by perturbation- evoked potentials (e.g., N1) and increase in beta frequency power when exposed to unpredicted perturbations. However, it is unknown how the pathology related to MCI (structural neural damage, reduced sensorimotor integration) affects reactive balance responses. Further, it is unknown if OAwMCI are capable of improving their reactive balance through repeated perturbations. Perturbation training has been introduced as a novel fall prevention paradigm involving repeated exposure to simulated balance disturbances (e.g., slips, trips), with robust effects on laboratory and real-life fall reduction. Trial-by-trial analyses indicate that CIOA can acquire motor adaptations in as little as 5 perturbation exposures, including improvements in biomechanical outcomes (fall rate, COM stability) and enhanced neuromuscular control (increased muscle synergy number). In theory, perturbation training could be implemented in OAwMCI to mitigate increased fall risk, however it is first necessary to assess 1) the magnitude of reactive balance impairment, and 2) the ability to acquire motor adaptations to repeated perturbations in this population. Thus, we propose a mechanistic investigation to determine differences in the biomechanical, neuromuscular, and cortical control of reactive balance between OAwMCI and CIOA when exposed to a novel treadmill gait-trip (Aims 1&2). We will also examine differences in the rate and magnitude of motor adaptation between OAwMCI and CIOA when exposed to 8 repeated treadmill gait-trips (Aim 3). The clinical impact of this study will be to mechanistically understand how pathology related to MCI may contribute to balance impairment and increased fall-risk. Further, with an understanding of how OAwMCI are able to adapt to repeated perturbations, this study will pave the road for the future design of effective perturbation training protocols that could significantly improve balance control and reduce fall incidence in OAwMCI.
