Postural tachycardia syndrome (POTS), is the chronic form of orthostatic intolerance associated with excessive upright tachycardia, and occurs predominantly in young females (>85%). Among its most troubling symptoms are lightheadedness, fatigue, and decreased memory often called "brain fog" by patients. Task-related neurovascular coupling (NVC) links neural activity to an increase in CBF known as "functional hyperemia". Although memory task performance and NVC deteriorated with angle of tilt in POTS but not healthy controls, cerebral blood flow (CBF) remained similar to control. Instead, the investigators observed extensive narrow band low frequency (0.07-0.13 Hz) oscillations in BP (OBP) that entrained and amplified oscillations in CBF (OCBF). OBP and OCBF increased with tilt angle and caused impaired working memory and reduced functional hyperemia. The cardiovagal baroreflex couples BP to HR to buffer BP changes. The investigators hypothesize that the cardiovagal baroreflex becomes progressively impaired with orthostasis in POTS, but not in healthy volunteers, and accounts for OBP, OCBF, and loss of NVC; further, improving the baroreflex reduces OBP, OCBF and Brain Fog in POTS.