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

In older adults, diminished sensation of the legs and feet is highly prevalent and causes poor balance and reduced mobility. This type of sensation is not only dependent upon the receptors and nerves in the legs and feet, but also upon a complex central nervous system pathway that includes the cerebral cortex of the brain. This project will use a form of noninvasive brain stimulation called transcranial direct current stimulation (tDCS) to test whether increasing the excitability of the brain networks that process sensory feedback can augment foot sole sensation, balance, and mobility in older adults suffering from mild-to-moderate foot sole sensory impairments.

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.