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.

Cerebral Vascular Control and Metabolism in Heat Stress

“…That brain temperature is warmer in the deeper compared to exterior regions has led some to believe that the human brain can selectively cool from the superficial surfaces in contact with the skull (65). Selective brain cooling (SBC), defined as a lowering of brain temperature below that of body core/aortic blood temperature, is well documented in certain mammals (29,30) and birds (216).…”

Thermal sensitivity to warmth during rest and exercise: a sex comparison

“…For females the areas around the head were significantly more sensitive than a large number of other locations, but particularly those areas within the leg region (p<0.05). The head has consistently been defined as a sensitive area due to the large number of thermoreceptors and the importance of keeping the brain within a thermo-prescriptive zone (Cabanac, 1993;Nadel et al 1973;Strughold andPorz, 1931, cited in Parsons, 2003 p59;Nagasaka et al 1998). The torso also contains vital organs and research has shown this to be an area less sensitive than the face but more sensitive than the extremities for various other parameters than studied here (Arens et al 2005;Cotter and Taylor, 2005;Havenith et al 2008;Nadel et al 1973;Nakamura et al 2008;Smith and Havenith 2012;Stevens et al 1974).…”

Brain cooling in humans ? anatomical considerations

“…For some authors (Brengelmann 1987) the copious and constant arterial blood flow to the brain appears sufficient to cool the brain under all conditions. Others (Cabanac 1993) concede that this concept may be correct for the conditions at normothermia, but they propose that an additional brain-directed cooling mechanism becomes effective during hyperthermia. These authors draw attention to vascular arrangements in humans, which permit effects comparable to SBC in "rete species".…”