Coupling between changes in human brain temperature and oxidative metabolism during prolonged visual stimulation

A fundamental discovery of modern human brain imaging with positron-emissio n tomography that the blood flow to activated regions of the normal human b rain increases substantially more than the oxygen consumption has led to a broad discussion in the literature concerning possible mechanisms responsib le for this phenomenon. Presently no consensus exists. It is well known tha t oxygen delivery is not the only function of systemic circulation. Additio nal roles include delivery of nutrients and other required substances to th e tissue, waste removal, and temperature regulation. Among these other func tions, the role of regional cerebral blood flow in local brain temperature regulation has received scant attention. Here we present a theoretical anal ysis supported by empirical data obtained with functional magnetic resonanc e suggesting that increase in regional cerebral blood flow during functiona l stimulation can cause local changes in the brain temperature and subseque nt local changes in the oxygen metabolism. On average, temperature decrease s by 0.2 degrees C. but individual variations up to +/-1 degrees C were als o observed. Major factors contributing to temperature regulation during fun ctional stimulation are changes in the oxygen consumption, changes in the t emperature of incoming arterial blood, and extensive heat exchange between activated and surrounding brain tissue.