The concurrent performance of two tasks, i.e., dual tasking (DT), is a common and ubiquitous every day phenomena. For example, people frequently walk while talking on a cellphone or drive while talking to a passenger. Often, the performance of one or more of these simultaneously performed tasks may deteriorate when another task is carried out at the same time, even in healthy young adults. This reduction in performance is referred to as the DT deficit or DT cost and is typically much higher in Idiopathic Fallers (IF) than in age-matched controls. In this population the DT cost impairs the gait pattern, as manifested, for example, in increased gait variability, exacerbating instability and fall risk.

In the proposed study, would be evaluated the effects of tDCS on dual tasking performance following tDCS.

The researchers expect that stimulation of the Pre Frontal Cortex (PFC) (using tDCS) will increase DT performance and prefrontal activation.

tDCS intervention: Noninvasive tDCS will be delivered by study personnel uninvolved with any other study procedures. In the study will be used a battery-driven electrical stimulator. Stimulation and sham condition will be performed based on previous studies. Briefly, the anode will be placed over the PFC and the cathode over the right supraorbital region. The real tDCS condition will consist of 20 min of continuous stimulation at target intensity of 1.5 mA. This amount of stimulation is safe for healthy young and older adults and has been shown to induce acute beneficial changes in cortical excitability and cognitive functions. For the sham condition, an inactive stimulation protocol would be followed, as compared with an 'off-target' active protocol, in order to minimize participant risk.

Pre- and post-tDCS assessments will include:

Gait assessment: Gait parameters will include both spatial and temporal parameters obtained using body fixed wearable sensors (accelerometers and gyroscopes) [Weiss et al. 2015; Ben et al. 2015]. Parameters will include (but are not limited to) gait speed, stride length and stride time as well as rhythmicity measures such as stride to stride variability and gait regularity.

Fall history and fear of falling will also be assessed (e.g., Falls Efficacy Scale International, FES-I) to further characterize the cohort and explore possible confounds.

Cognitive assessment: A detailed computerized cognitive battery that has been used extensively at TASMC in different cohorts [Dwolatzky et al. 2003;Hausdorff et al. 2006;Springer et al. 2006;Yogev et al. 2005;Aarsland et al. 2003] will quantify several cognitive domains including working memory, executive function, verbal function, problem solving, a global cognitive score, and attention.

Inclusion Criteria:

1. age 65-85 years,
2. ability to walk for 6 minutes unassisted,
3. adequate vision capabilities, and
4. stable medications for the past month.

Exclusion Criteria:

1. diagnosis of stroke, Parkinson's disease, peripheral neuropathy or other neurologic disorder,
2. lower-extremity deformity, joint replacement, severe arthritis or other diagnosed musculoskeletal disorder that may influence gait,
3. orthostatic hypotension, recent history of syncope or vertigo,
4. myocardial infarction or surgery within the past 6 months,
5. any unstable medical condition,
6. psychiatric co-morbidity (e.g., major depressive disorder as determined by DSM V criteria),
7. likely dementia (i.e., Mini Mental State Exam score < 24 or based on DSM V),
8. sedating medications (sedatives, anti-psychotics, hypnotics, anti-depressants,
9. colorblindness (confounder for cognitive assessment), or
10. contraindications to tDCS