RecruitingDevice studyNeural Control of Gait & Navigation in ADRDBrain network segregation, or independent functioning, declines with age and is associated with slower walking speed. Here, the investigators will determine the extent to which brain vestibular network segregation can be altered with bilateral vestibular cortical transcranial direct current stimulation (tDCS) in older adults with subjective cognitive decline. Participants will be randomly assigned to an active or sham stimulation condition. They will receive three, 20-minute sessions of tDCS while they are walking and performing cognitive tasks. MRI of the brain will be acquired before and after these three sessions.