Basic aspects of functional brain metabolism.

Brain energy metabolism and blood flow are greatest in neuropil where there is a high density of oxidative enzymes and capillaries. Here fluctuations in synaptic potentials cause the greatest demand on metabolism through the continuous need to pump ions to maintain membrane charge. A transient increase in functional activity within a pathway causes an increase in energy metabolism followed by an increase in blood flow. The vascular response is biphasic, with an initial increase followed by a plateau phase. The site and magnitude of the response reflect the quality and intensity of the stimulus. Prolonged changes in functional activity within a pathway cause a reorganization of energy metabolizing enzymes and vascular architecture.