Coupling of blood flow and metabolism in the brain.

Blood flow and metabolism are locally heterogeneous in the brain, but tightly coupled. This adjustment occurs in two different ways: (1) short-term, dynamic coupling mediated by local vasoactive factors that ensure second-to-second regulation; (2) long-term, static coupling, apparently mediated by capillary density and developed in response to local functional and metabolic activity. Recognizing these two mechanisms permits one to distinguish apparent from real uncoupling. It allows the conclusion that there is no indication of an uncoupling of metabolism and blood flow during physiological conditions.