RecruitingVascular mEchanisms in, Stroke, dePression, dementiA, and deliRum: The VESPAR ProjectThe goal of this observational study is to determine the feasibility of using integrated Transcranial Doppler Ultrasonography or Near Infrared Spectroscopy to detect changes in cerebral autoregulation and neurovascular coupling in healthy, stroke, dementia, depression and delirium populations. We also aim to: * Determine the optimal stimulus for neurovascular coupling * To derive sample size estimates for a future study * To develop a multilevel, multivariate model that can be applied to future datasets