Neuromechanisms of falls in older adults with MCI: Targeting assessment and training of reactive balance control

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Mild cognitive impairment (MCI) occurs along a continuum from normal cognition to dementia and affects nearly a quarter of individuals 70-79 years old, with the prevalence drastically increasing each decade after. Although most older adults with MCI (OAwMCI) are independent in their daily living, they are known to have significantly greater likelihood of falls compared to their cognitively intact counterparts. In addition to cognitive deficits, persons with MCI can experience motor dysfunction, including deficits in gait and balance. While changes in stance posture control and gait functionality have been thoroughly investigated in this population, reactive balance control and protective stepping responses that are recruited to recover from unpredictable, larger external perturbations have not yet been extensively examined. Additionally, though OAwMCI show slower adaptation and motor learning in comparison to their healthy counterparts, it remains to be unknown whether OAwMCI can adapt to task-specific training via repeated exposure to unpredicted perturbations as healthy older adults (OA) do. Furthermore, it is well established that OAwMCI have worse dual-task performance during both stance and gait. This presentation is related to impaired executive function, visuomotor function and spatial awareness. However, dual-task performance during perturbed stance and gait in association with increased fall-risk has not yet been investigated in OAwMCI. In addition, it is well-established that higher cortical centers play a vital role in modulation of reactive balance control. Interestingly, in OAwMCI, the decline in volitional balance control under sensory and cognitive challenges is corelated to an increased resting state activation of the default mode network, reduced white matter integrity and reduced gray matter volume. However, there is limited evidence examining the association between impaired structural integrity and neural correlates with reactive balance control measures and resulting higher occurrence of falls in this population. Our previous research has shown that two key variables, reactive control of stability and vertical limb support, contribute to more than 90% of laboratory slip-falls in OA. Thus, improving these key variables can contribute to significant reduction in fall risk in OA. However, such task-specific intervention-based studies are lacking in the MCI population. To fill the gap in the literature, our study proposes to investigate the differences in neuromechanics of reactive stepping responses to externally-induced balance perturbations in OAwMCI compared to OA. Further, our study proposes to relate reactive stability control to changes in brain structural and functional connectivity. Lastly, our study proposes to determine the effect of a novel task- specific perturbation-based cognitive-motor intervention for enhancing fall-resisting skills in OAwMCI.