Remote tDCS and Chair Yoga for Chronic Knee Pain in Alzheimer's Patients

Inclusion Criteria (participants): * Live in the community (not institutionalized). * Have a diagnosis of Alzheimer's disease and related dementias (ADRD), including Alzheimer's disease, Lewy Body Dementia, Vascular Dementia, or Multiple Etiology Dementias (MED) diagnosed by a neurologist or other healthcare provider. * Be in mild to moderate ADRD, as indicated by a Quick Dementia Rating Scale (QDRS) score between 6 and 20.5. * Score above 10 on the Montreal Cognitive Assessment (MoCA). * Experience chronic knee pain (caregiver-reported average pain in the past 3 months \> 40 out of 100). * Have no planned changes to their medication regimen or other interventions for knee pain during the trial. * Agree to participate in both transcranial direct current stimulation (tDCS) and online chair yoga (OCY). * Be able to ambulate independently with minimal assistance (e.g., using a cane or walker) for participation in OCY and the Timed Up and Go (TUG) test. - -- Be English-speaking and able to understand verbal instructions (literacy not required). * Be able to consent for themselves or identify a legally authorized representative who can provide written informed consent. * Exhibit neuropsychiatric symptoms (e.g., apathy, agitation). * Be naïve to yoga and tDCS. Exclusion Criteria (participants): * a history of brain surgery, brain tumor, head trauma, seizure/epilepsy, stroke, cancer affecting the head, or intracranial metal implantation; * systemic rheumatic disorders, including rheumatoid arthritis, systemic lupus erythematosus, or fibromyalgia; * prosthetic knee replacement or non-arthroscopic surgery to the affected knee; * compromised skin integrity on the head in the area where electrodes will be placed; * serious comorbidities that preclude participation in tDCS or OCY (e.g., heart failure \[level IV\] causing shortness of breath on exertion); * hospitalization within the preceding year for neuropsychiatric illness that would impact knee pain or interfere with study procedures; * use of another neurostimulation device (e.g., spinal cord stimulator, cardio-stimulator, or implanted cardioverter-defibrillator). Inclusion Criteria (caregivers): A caregiver is defined in this study as the person who provides care and assistance to a patient with ADRD (e.g., helping with daily activities, managing medications, ensuring safety). * Caregivers must be at least 18 years old * have provided care and assistance to the patient for at least 10 hours per week at the time of enrollment * anticipate continuing to provide care and assistance for the next 4 months (until the study ends) * be willing to receive tDCS training, administer home-based tDCS sessions, and assist the patient in attending OCY sessions * have access to a reliable Internet connec¬tion for secure videoconferencing for real-time remote supervision * English-speaking caregivers who can understand verbal instructions. Exclusion Criteria (caregivers): * alcohol/substance use disorder * inability to understand English * disability that would prevent assisting patients with ADRD from participating in tDCS and OCY (e.g., blindness, deafness) * unwillingness to provide care and assistance to patients until the study is completed. * If caregiver does not meet the inclusion/exclusion criteria, the participant will not be accepted into the study.