Mild Cognitive Impairment (MCI) represents a common prodromal phase of dementia1. As compared to older adults who are cognitively-intact, those with MCI tend to exhibit poor "dual-task" standing balance performance; that is, the ability to maintain balance when standing and simultaneously performing an unrelated cognitive task. Moreover, those older adults who have worse dual-task standing balance are more likely to suffer falls and develop dementia. As such, strategies designed to understand and enhance the brain functionality involved in dual-task standing balance hold great promise to improve daily life function, and potentially, reduce the risk of dementia in this population.

Surface electroencephalography (EEG) allows non-invasive assessment of brain activity dynamics over short periods of time, even when standing. It has been demonstrated in younger and older adults that dual-task standing is associated with brain activity fluctuations at specific frequencies. A recent study from our laboratory demonstrated that in older adults, 1) performance of a serial subtraction cognitive task when standing reduces fronto-central alpha power (i.e., fluctuations in the 8-13 Hz band), and 2) those with lower fronto-central alpha power when dual tasking exhibit worse dual task standing balance. Intriguingly, numerous studies have separately linked diminished alpha activity with worse performance on executive function and visuomotor tasks, as well as global cognitive decline in older adults. We therefore contend that therapeutic strategies designed to increase alpha activity hold promise to improve dual-task standing performance, and many other cognitive-motor functions in older adults with and without MCI. To date, however, the effects of enhancing fronto-central alpha activity to improve dual-task balance in older adults with and without MCI have not been studied.

Transcranial alternating stimulation (tACS) is a safe, non-invasive brain stimulation technique that utilizes low-amplitude alternating currents to modulate brain activity and entrain specific cortical rhythms depending on the applied stimulation frequency. Targeting alpha band (10 Hz) in the frontal region has been shown to improve cognitive functioning in healthy older adults. However, no studies have investigated the effect of 10 Hz fronto-central stimulation on EEG alpha activity and postural sway outcomes during dual-task standing in older adults with and without MCI. We thus propose to conduct a within-subject cross-over, sham-controlled study in 30 older adults without an overt disease and 30 older adults with MCI. Participants will undergo dual-task standing and cognitive assessments immediately before and after single sessions of 10 Hz tACS (fronto-central alpha stimulation), and active-sham to understand the effect of different stimulation parameters on dual-task standing performance in older adults. We hypothesize that (1) older adults with MCI will demonstrate decreased EEG alpha power during dual-task standing compared to healthy controls, and decreased alpha power will be associated with worse balance outcomes during dual-task standing, and (2) compared to the pre-stimulation condition, participants will exhibit a greater increase in alpha power during the dual-task standing condition following tACS as compared to sham stimulation, and the increase in alpha power from pre-to-post tACS will correlate with a decrease in dual-task postural sway speed from pre-to-post tACS in older adults with and without MCI.