Natural selective cooling of the human brain: evidence of its occurrence and magnitude.

1. The technique of perceptual rating of thermal stimuli was used, in eight human subjects immersed in warm water, in order to appreciate whether they were hypo-, normo- or hyperthermic. Oesophageal, tympanic and forehead skin temperatures were recorded, as also was the temperature of the skin above the angularis oculi vein. Once the subjects gave clearly hyperthermic ratings, one arm was exposed to a 6 m/s wind. After 5--10 min the arm was re-immersed and the face was fanned. 2. Fanning of the arm resulted in lowering of body core temperature. However ratings of thermal stimuli remained hyperthermic. 3. Face fanning decreased forehead skin, angularis oculi vein and tympanic temperatures. Hyperthermic ratings were replaced by normothermic ratings, although oesophageal temperature continued to rise. 4. The upper limit of oesophageal temperature for normothermic ratings was 37.o6 +/- 0.09 degrees C during the control period without fanning. This temperature rose to 37.91 +/- 0.09 degrees C during facial ventilation. 5. These results suggest a selective cerebral cooling due to venous blood returning from facial skin via the ophthalmic vein to the cavernous sinus, where a cooling of arterial blood ascending to the brain can take place.