Brain Stimulation for Foot-sole Sensation in Older Adults With Foot-sole Somatosensory Deficits

Inclusion Criteria:

1. Aged ≥65 years.
2. Self-reported feeling of unsteadiness or difficulty when standing and walking.
3. Mild-to-moderate foot-sole somatosensory impairment: the ability to perceive 75g monofilament but inability to perceive 10g monofilament.

Exclusion Criteria:

1. self-reported inability to stand or walk continuously for one minute without personal assistance (canes or walkers allowed);
2. history or presence of foot ulceration, amputation, or deformities;
3. self-reported uncontrolled pain or pain that is associated with mobility disability;
4. uncontrolled diabetes mellitus;
5. hospitalization within the past three months due to acute illness, or as the result of a musculoskeletal injury significantly affecting balance;
6. persistent severe pain of lower extremity when standing or walking;
7. diagnosis of dementia, Parkinson's disease, or stroke that affects balance;
8. unstable medical condition;
9. legal blindness or deafness;
10. uncontrolled hypertension (i.e., systolic BP \>180, diastolic BP \>100 mm Hg, or prescription of ≥3 anti-hypertensive medications);
11. functionally limiting nephropathy, severe diseases or transplant of the kidney or liver, renal or congestive heart failure;
12. active cancer treatment;
13. balance disorders due to past use of chemotherapy or history of Guillain-Barré syndrome;
14. use of neuro-active or recreational drugs (e.g., sedatives, anti-psychotics), or alcohol abuse, which may affect the brain excitability;
15. contraindications to MRI or tDCS (e.g., personal or family history of seizures or epilepsy, metallic or electric bio-implants, claustrophobia, brain surgery);
16. persistent vertigo;
17. history of Charcot-Marie-Tooth nerve disease.