Cerebello-Cortical Connectivity and Balance Adaptation in Younger and Older Adults

This study will investigate how communication between the cerebellum and cerebral cortex contributes to balance control and adaptation in younger and older adults. The study will enroll healthy younger adults ages 21-35 years and older adults ages 65-95 years. Participants will complete a single testing session that includes clinical balance assessments, transcranial magnetic stimulation (TMS), electroencephalography (EEG), electromyography (EMG), and reactive balance testing using an instrumented treadmill. Cerebello-cortical connectivity will be measured before and after reactive balance testing using cerebellar brain inhibition (CBI) and the cerebellar TMS-evoked potential P80. The study will examine how these measures relate to cortical activity, balance recovery, and adaptation across repeated perturbations, and whether these relationships differ between younger and older adults.

Inclusion Criteria: * Adults aged 21-35 years (younger adult group) or 65-95 years (older adult group). * Willing and able to participate in and comply with all study procedures. * Able to provide informed consent and communicate with study researchers. * English-speaking. * No major orthopedic disability. * Vision of 20/40 or better, with or without corrective lenses, by self-report. * Able to stand for 10 minutes and walk 10 meters with or without an assistive device, without assistance from another person. Exclusion Criteria: * History of seizure, epilepsy, or convulsion in the participant or an immediate family member. * Current use of antiepileptic medications. * Metal or electrical implant in the head, neck, or chest, other than dental work. * Any other contraindication identified on the TMS safety screening form. * Pregnancy. * Neurological diagnosis including stroke, Parkinson's disease, multiple sclerosis, Alzheimer's disease, cerebellar ataxia, or other progressive movement disorders. * Insulin-dependent diabetes. * Peripheral neuropathy. * Significant sensory impairment affecting balance or cognition, including visual, vestibular, or auditory impairment. * Active dermatitis, infection, or open wounds on the head or scalp. * Head injury or concussion within the previous year. * Lower-extremity joint replacement or major orthopedic surgery within the previous year.