 This region functions in the regulation of fluid and electrolyte balance by controlling thirst, sodium excretion, blood volume regulation, and vasopressin secretion.The VOLT is one of the four sensory circumventricular organs providing information to other brain regions (others are median eminence, subfornical organ, and area postrema).VOLT capillaries do not have a blood-brain barrier, and so neurons in this region can respond to circulating factors present in the systemic circulation.