The study investigates the role of pericytes in regulating capillary diameter in the central nervous system (CNS). Pericytes, which are apposed to CNS capillaries and contain contractile proteins, are shown to control capillary constriction in both retinal and cerebellar slices. Electrical stimulation of retinal pericytes evokes a localized capillary constriction that propagates at a speed of ~2 μm/sec to distant pericytes. ATP and noradrenaline, acting through P2Y receptors, cause capillary constriction, while glutamate reverses this effect. In simulated ischemia, some pericytes constrict capillaries. These findings suggest that pericytes modulate blood flow in response to neural activity, potentially contributing to functional imaging signals and CNS vascular diseases. The study challenges the traditional view that arterioles are solely responsible for the blood flow increase evoked by neural activity.The study investigates the role of pericytes in regulating capillary diameter in the central nervous system (CNS). Pericytes, which are apposed to CNS capillaries and contain contractile proteins, are shown to control capillary constriction in both retinal and cerebellar slices. Electrical stimulation of retinal pericytes evokes a localized capillary constriction that propagates at a speed of ~2 μm/sec to distant pericytes. ATP and noradrenaline, acting through P2Y receptors, cause capillary constriction, while glutamate reverses this effect. In simulated ischemia, some pericytes constrict capillaries. These findings suggest that pericytes modulate blood flow in response to neural activity, potentially contributing to functional imaging signals and CNS vascular diseases. The study challenges the traditional view that arterioles are solely responsible for the blood flow increase evoked by neural activity.