Verifying the physiological significance of the preference for low facial temperature in humans

Objectives Regional differences in thermal pleasantness have been reported; local cooling of the head induces pleasantness during mild heat exposure. However, the physiological significance of these effects remains unclear. This study tested the hypothesis that facial or neck cooling could selectively decrease brain temperature (selective brain cooling; SBC). Methods Eight male volunteers participated in normothermic and hyperthermic protocols, comprising a 10-min baseline, 15-min cooling, and 15-min post-cooling period. During cooling, facial fanning (FAN face ), forehead conductive cooling (COND head ), neck conductive cooling (COND neck ), or control without cooling (NO-C) was performed. In the hyperthermic protocol, the participants performed cycling exercises at 60% heart rate reserve until oesophageal temperature (T es ) rose by 1°C. The difference between tympanic temperature (T ty ) and T es was used as an index of brain cooling. Results Under normothermic conditions, no significant difference was observed between T ty and T es in any trial. Under hyperthermic conditions, T ty was significantly lower than T es after facial fanning, with the largest difference at 10 min (T ty = 37.6±0.3°C; T es = 37.7±0.3°C; P = 0.001, Cohen’s d = 2.021); the brain-cooling index (T es –T ty ) was 0.08±0.04°C. No significant differences occurred in the NO-C, CONDhead, or CONDneck trials. These results suggest that facial fanning should contribute slightly to brain cooling in hyperthermic individuals. Conclusion A preference for low facial temperature should help cool the brain. However, this brain cooling effect should be minimal compared with SBC in animals possessing carotid rete. SBC in humans could not be validated by the results in this study.