Objective To analyze changes in sleep,mood state,and brain function in healthy populations living in near-sea-level environments before and after exposure to high-altitude environment,and to explore the correlations between regional brain functional changes and variations in sleep and mood states.Methods A total of 45 healthy volunteers were enrolled.The participants came from regions of near-sea-level altitudes and were exposed to the high-altitude environment for a short period of time.The Pittsburgh Sleep Quality Index(PSQI),Zung Self-Rating Depression Scale(SDS),Patient Health Questionnaire-9(PHQ-9),Zung Self-Rating Anxiety Scale(SAS),and Generalized Anxiety Disorder-7(GAD-7)were administered to assess sleep quality as well as depressive and anxiety symptoms at 4 time points—prior to high-altitude exposure,immediately after exposure,one month after returning to low-altitude regions,and three months after returning to low-altitude regions.Resting-state functional magnetic resonance imaging(rs-fMRI)data were collected before and after high-altitude exposure,and regional brain functional parameters,including the amplitude of low-frequency fluctuations(ALFF)and functional connectivity strength,were analyzed.Statistical analyses were performed,including a linear mixed-effects model to evaluate longitudinal changes in scale scores,paired-sample t-tests to compare brain function differences before and after exposure,and Pearson correlation analyses to examine the relationship between brain functional changes and alterations in sleep and mood states.Results Compared with the pre-exposure findings,the participants exhibited significantly increased PSQI scores(8.89±4.41 vs.5.08±2.69,P<0.05)and PHQ-9 scores(3.60±4.19 vs.1.54±2.30,P<0.05)immediately after high-altitude exposure.One month after returning to the low-altitude environment,both sleep and depression scores decreased relative to the findings immediately after exposure(PSQI:3.88±2.13 vs.8.89±4.41,P<0.05;PHQ-9:1.50±2.25 vs.3.60±4.19,P<0.05)and showed no statistically significant difference compared with the pre-exposure findings(P>0.05).Three months after returning to near-sea-level environment,sleep,depression,and anxiety scores were all reduced compared with the findings immediately after exposure(PSQI:3.76±2.31 vs.8.89±4.41,P<0.05;PHQ-9:1.24±2.13 vs.3.60±4.19,P<0.05;SAS:23.84±5.93 vs.27.93±7.05,P<0.05),also showing no significant difference compared with the pre-exposure levels(P>0.05).Brain function analysis revealed that,relative to the pre-exposure levels,ALFF in the bilateral superior temporal gyrus,insula,and dorsolateral prefrontal cortex(DLPFC)increased after high-altitude exposure(P<0.05),and that functional connectivity strength in the DLPFC was also elevated(P<0.05).Furthermore,changes in DLPFC functional connectivity strength were positively correlated with changes in sleep and mood scores(P<0.05).Conclusion High-altitude exposure has a significant impact on the sleep,mood states,and brain function of populations from near-sea-level regions,and DLPFC,in particular,is closely associated with changes in sleep and mood states.The findings of this study provide a theoretical basis for health management and intervention strategies in high-altitude environments.