The study investigates the role of capillary pericytes in regulating cerebral blood flow (CBF) in both health and disease. Pericytes, which are contractile cells surrounding capillaries, are found to actively relax and dilate capillaries in response to neuronal activity and glutamate, a neurotransmitter. This dilation is mediated by prostaglandin E2 (PGE2) and requires nitric oxide (NO) to suppress vasoconstrictive 20-HETE synthesis. In vivo, capillaries dilate before arterioles when sensory input increases blood flow, contributing 84% of the total increase. In pathology, ischemia causes capillary constriction and subsequent pericyte death, leading to long-lasting capillary constriction and potential neuronal damage. The study highlights the importance of preventing pericyte constriction and death to reduce the long-term decrease in blood flow after stroke.The study investigates the role of capillary pericytes in regulating cerebral blood flow (CBF) in both health and disease. Pericytes, which are contractile cells surrounding capillaries, are found to actively relax and dilate capillaries in response to neuronal activity and glutamate, a neurotransmitter. This dilation is mediated by prostaglandin E2 (PGE2) and requires nitric oxide (NO) to suppress vasoconstrictive 20-HETE synthesis. In vivo, capillaries dilate before arterioles when sensory input increases blood flow, contributing 84% of the total increase. In pathology, ischemia causes capillary constriction and subsequent pericyte death, leading to long-lasting capillary constriction and potential neuronal damage. The study highlights the importance of preventing pericyte constriction and death to reduce the long-term decrease in blood flow after stroke.