Zap your brain at home to fight dementia?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Men and women * Age 65-90 years * Subjective cognitive complaints as defined by a 'Yes' response to "Do you feel that you have more problems with memory than most?" or a 'No' response to "is your mind as clear as it used to be?" * Montreal Cognitive Assessment (MoCA) score ≥21 * Slow gait speed as measured by averaging two 4-Meter walks and defined as a usual walking speed one standard deviation below age and sex-adjusted means. * Absence of significant disability as defined by the ability to walk over the instrumented gait mat unassisted (e.g., able to walk without any walking aids for at least 2 minutes non-stop) and preserved activities of daily living as defined by a score of less than 9 on the Functional Activities Questionnaire. * Identification of an eligible informant * Identification of a willing and able tDCS-administrator; i.e., a study partner to lead the administration of home-based transcranial direct current stimulation (tDCS) * Access to reliable WiFi in the participant's home Exclusion Criteria: * Formal education less than the 8th grade * Previous physician diagnosis of dementia * Any current diagnosis of a major psychiatric disorder (e.g., schizophrenia, bipolar disorder, major depressive disorder) * Evidence of moderate-to-severe depressive symptoms defined by a score of ≥9 on the 15-item Geriatric Depression Scale * History of head trauma resulting in prolonged loss of consciousness * History of fainting spells of unknown or undetermined etiology that might constitute seizures * History of seizures, diagnosis of epilepsy, or immediate (first-degree relative) family history of epilepsy except for a single seizure of benign etiology (e.g. febrile seizures) in the judgment of a board-certified neurologist * Hospitalization within the past three months due to acute illness, or as the result of a musculoskeletal injury significantly affecting gait or balance * Any unstable medical condition or chronic (particularly) uncontrolled medical conditions that may cause a medical emergency in case of a provoked seizure (cardiac malformation, cardiac dysrhythmia, asthma, etc.) or study complication * Substance use disorders within the past six months * A hairstyle or headdress that prevents electrode contact with the scalp or would interfere with the stimulation (for example thick braids, hair weave, afro, wig) * Chronic vertigo * Myocardial infarction within the past 6 months * Active cancer for which chemo-/radiation therapy is being received * Legal blindness * Visual hallucinations (history or self-report) * Pacemaker * Contraindications to MRI or tDCS, including unprovoked seizure within the past two years, risk of ferromagnetic objects anywhere in the body, self-reported presence of specific implanted medical devices (e.g., deep brain stimulator, medication infusion pump, cochlear implant, pacemaker, etc.), the presence of any active dermatological condition, such as eczema, on the scalp, etc. as outlined by current recommendations for noninvasive brain stimulation endorsed by the International Federation for Clinical Neurophysiology. * History of REM sleep behavior disorder (RBD), often an early sign of Parkinson's disease * Medications and medical history will be reviewed by the responsible covering physician and a decision about inclusion will be made based on the participant's past medical history, drug dose, history of recent medication changes or duration of treatment, and combination with other CNS active drugs.