The concept of coupling blood flow to brain function: revision required?

A tight coupling exists between brain function and cerebral perfusion in most situations. The Roy and Sherrington hypothesis has been widely accepted to account for the phenomenon: increased neuronal metabolic activity will give rise to the accumulation of vasoactive catabolites, which decrease vascular resistance and thereby increase blood flow until normal homeostasis is reestablished. However, the hypothesis does not account for the disproportionate increase in flow that occurs in a number of circumstances. There are additional difficulties in reconciling more recent experimental data with the Roy and Sherrington hypothesis. In this review we direct attention toward the rich perivascular nerve supply to all parts of the cerebral circulation as possibly being an alternative control system allowing for rapid parallel changes in flow and neuronal activity.