Standing and walking are almost always completed in unison with other mental tasks such as talking, reading or problem solving. The ability to safely perform this important type of “dual tasking” is dependent upon one's capacity to effectively activate the appropriate brain networks involved in both motor and cognitive function. In older adults who have suffered recent, otherwise unexplained falls, such dual tasking significantly interferes with the control of standing or walking. We thus contend that strategies designed to facilitate brain activation within cognitive-motor brain networks hold great potential to reduce dual task costs, enhance numerous other aspects of physical and cognitive function, and ultimately, reduced falls in older adults. Transcranial direct current stimulation (tDCS) is a safe, noninvasive technology that can selectively enhance brain excitability (i.e., the likelihood of activation) by passing low-level currents between electrodes placed upon the scalp. We have demonstrated in a series of ground-breaking studies that tDCS targeting the left dorsolateral prefrontal cortex (dlPFC)—a primary brain region involved in cognitive “executive” function—incudes lasting improvements in dual task performance and mobility in older adults. Still, the optimal brain region(s) to target with tDCS, and the duration of benefits induced by multi-session tDCS interventions, are unknown. Moreover, to date, tDCS delivery has attempted to optimize current flow based on modeling of a “typical” brain and has thus not been personalized to individual differences in the anatomy of the aging brain. We will conduct a randomized, sham-controlled, double-blinded trial with a 6-month follow-up period to compare the effects of 4 different personalized, multisession tDCS interventions on the dual task costs to standing and walking (Aim 1), as well as other physical (Aim 2) and cognitive (Aim 3) factors on the causal pathway to falls that are important to everyday function, in older adults with previous falls. We will recruit 120 men and women (30 per intervention arm) aged 65-85 years with two or more falls within the past year, who are fearful of falling again, yet have no major neural or musculoskeletal disorders. tDCS interventions will entail 20 sessions over a four-week period targeting 1) the left dlPFC only; 2) the bilateral primary motor cortex (M1, leg regions) only; 3) both of these regions simultaneously; or 4) neither of these regions (i.e., sham). We will utilize current flow modeling of baseline structural MRIs to customize tDCS electrode placement and stimulation parameters to optimize current flow to the desired target(s) within each participant's brain. We hypothesize that multi-focal tDCS designed to simultaneously increase functional activation of motor and cognitive networks will have the greatest benefits on dual tasking and other important physical and cognitive outcomes on the causal pathway to falls in this vulnerable population o...