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

Inclusion criteria

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

Exclusion criteria

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