Selective brain cooling in humans: "fancy" or fact?

Abstract

A mechanism that selectively cools the brain during hyperthermia is a well-accepted fact in animals. Selective brain cooling (SBC) during hyperthermia has also been proposed in humans, but this suggestion has met with considerable debate. Several authors have rejected the idea of human SBC for the following reasons: 1) SBC is illogical because this mechanism removes the error signal activating the defense against hyperthermia; 2) unlike other animals, humans do not pant and thus do not possess a powerful heat sink at a short distance from the brain; 3) humans do not have a carotid rete, the countercurrent heat exchanger between the arterial and venous bloods flowing in and out of the brain; 4) the high and constant arterial blood flow of the brain is sufficient to cool the brain under all conditions; and 5) the relatively low tympanic temperature (Tty) recorded in hyperthermic humans is not a sign of SBC, but rather is the sign of contamination of Tty by a low head skin temperature. These arguments are reviewed and rejected and results of several recent experiments are summarized. Finally, recent experimental articles that contradict the existence of human SBC or the validity of Tty are discussed and their conclusions refuted. This review points to overwhelming evidence in favor of human SBC.