The Effects Of Head-cooling On Brain Function During Passive Hyperthermia: An Resting-fMRI Study

ObjectiveTo investigate the effect of head-cooling on resting-state spontaneous brain activity and network-level brain function during passive hyperthermia using amplitude low frequency fluctuations(ALFF)and functional connectivity(FC),respectively.These may provide several neurological evidence that head-cooling protect brain function during hyperthermia.Methods1.ParticipantsA total of 18 healthy right handed young male subjects(23.6±3.4 years,ranging from 20 to 28 years)took part in the present study.All of the participants were free of any neurological or psychiatric diseases and never participated in any hyperthermia experiments before.2.ProcedureUsing a counter-balanced design,each participant must completed three experimental trials in a normal control condition(NC,25 °C)and two conditions in a hot environment(50 °C)with(HHC)or without(HOT)keeping the head cool.Experiments on the same participant were performed at the same time on different days,separated by at least 1 week.The participants covered the whole body as well as the head entered the environmental chamber and remained in a sitting posture,the temperature was set at 25°C /or 50°C before.In addition,a cold hat filling with cold storage material(5 °C)was put on the head under HHC condition.After 50 min,the participants were taken to the adjacent MRI room for scanning.During the 10 min scans,the pipeline in the suit was connected to a subsidiary water temperature control device,with water circulating(25 °C /or 50 °C)throughout the pipeline.In total,each participant endured heat exposure for approximately 1 hour.All participants had rights to discontinue the experiment.Rectal temperature and net weight of each participant were recorded before and after the experiments using a rectal temperature logger and an electronic scale.Visual analog scale(VAS)test was performed to evaluate the subjective replies concerning the temperature sensation and thermal comfort sensation after the scan.The reference points were given as follows;0: very cold/ very uncomfortable,2.5:cold/uncomfortable,5: neutral,7.5: hot/ comfortable,10 : very hot/ very comfortable.3.Data acquisitionThe resting-state data were obtained from all participants using a 3T MRI system with an eight-channel head coil.During the MRI scan,the participants was instructed to lie in a supine position and remain motionless with their eyes closed and without concentrating on anything in particular.The scanning sequences included routine sequences(T1WI ? T2WI)and blood oxygen level-dependent(BOLD)sequence.4.Data preprocessingData preprocessing was performed using SPM8 package and REST1.8 on the MATLAB R2008 a platform.5.Data analysisAll the statistical analyses were conducted using SPSS 18.0.A repeated measures analysis of variance(ANOVA)was performed to explore the differences of ALFF values?subjective sensation and rectal temperature among the three conditions.Pearson's correlation analyses was performed to explore the relationships between the subjective sensation scores and ALFF values in each brain region.All the reported data were presented as mean ± SD and statistical significance was accepted at P < 0.05.ResultsBrain 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.Conclusions1.There are anti-correlated and competitive relationships between two key nodes of the DMN(MPFC/ACC,PCC/PCu)and right fusiform gyrus;We hypothesized that increased activity in the fusiform gyrus can be a compensatory for decreased activity in the DMN by enhancing anti-correlation between the DMN and the visual networks during passive hyperthermia.2.Head-cooling could substantially reduce the negative effect of hyperthermia on human brain activity.3.Head-cooling significantly improved feelings of thermal comfort and played a part in decreasing hot sensation passive hyperthermia.