The effects of head-cooling on brain function during passive hyperthermia: an fMRI study.

PURPOSE: To investigate the effect of head-cooling on resting-state spontaneous brain activity during passive hyperthermia. METHODS: An environmental heat exposure was simulated on 16 healthy men under a normal control condition (NC) at 25 °C and two hot conditions at 50 °C with hyperthermia with head-cooling condition (HHC) and without hyperthermia condition (HOT) keeping the head cool, respectively. Resting-state functional MRI (fMRI) data were acquired under each condition and the values of amplitude low frequency fluctuations (ALFF) and z functional connectivity (zFC) were computed to examine regional activity and functional integration, respectively. Pearson's correlation analysis between the ALFF value and subjective sensations scores were performed. RESULTS: Brain regions with significant ALFF differences among the three conditions were found primarily in the right medial prefrontal cortex/anterior cingulate cortex (MPFC/ACC), bilateral posterior cingulate cortex/precuneus (PCC/PCu), and right fusiform gyrus. Compared to the NC or HOT condition, the HHC condition exhibited significantly increased ALFF in the bilateral PCC/PCu and decreased ALFF in the right fusiform gyrus. However, ALFF of the right MPFC/ACC showed no significant difference between the NC and HHC conditions. Positive FC between the right MPFC/ACC and bilateral PCC/PCu was significantly increased in HHC condition with respect to HOT condition. Negative FC between the right fusiform gyrus and the right MPFC/ACC, bilateral PCC/PCu was observed with a decreasing trend from the HHC condition to the HOT condition. Moreover, head-cooling also improved thermal comfort during passive hyperthermia. CONCLUSIONS: Head-cooling could substantially reduce the negative effect of hyperthermia on human brain activity as well as thermal sensation.