The metabolic requirements of functional activity in the human brain: a positron emission tomography study.

In the resting state it is well established that the energy demands of the mammalian brain are met by the oxidation of glucose (Siesjo, 1978). Changes in the functional activity of the brain (e.g., motor activity, speech, vision, audition, somesthesis) are accompanied by increases in local blood flow and glucose utilization (for a review of this extensive literature see Raichle, 1987). It had been generally assumed that the energy demands accompanying these phasic changes in neural activity were also supported by glucose oxidation supporting the large energy expenditures required to maintain membrane ionic gradients. The increase in local blood flow had been considered a response to oxygen depletion and metabolite excess in the form of carbon dioxide.