Chronic hypoxia reshapes the brain: subregional volume reductions of the hippocampus and amygdala contrasts with behavioral resilience in long-term high-altitude migrants

Background Individuals relocating from low- to high-altitude areas typically encounter serious health challenges due to harsh environmental conditions. Although individual adaptation varies, cognitive decline and mental health disturbances are common in these migrants. This study sought to comprehensively investigate the morphological changes of hippocampal and amygdalar subregions in long-term migrants transitioning from low to high altitudes. Methods Forty-four young adult male Han Chinese low-to-high-altitude migrants (HAs) and 44 age-matched male low-altitude Han Chinese residents (LAs) underwent three-dimensional high-resolution structural magnetic resonance imaging and neuropsychological testing. Gray matter volume at both hemispheric and hippocampal/amygdalar subregional levels was calculated. The relationships between altered subregional volumes and neuropsychological performance in HAs were then analyzed. Results Compared with that of the LA group, the gray matter volume of the HA group was basically maintained at the bilateral cerebral cortex and cerebellar cortex but significantly reduced in multiple hippocampal and amygdalar subregions. Moreover, longer residence at high altitude was associated with fewer insomnia symptoms. Additionally, volume decreases in specific hippocampal and amygdalar subregions in the HA group were significantly related to the severity of insomnia and the duration of high-altitude exposure. Conclusion Our findings reveal complex patterns of gray matter alterations in long-term HAs. The correlations among specific morphological changes, duration of high-altitude residency, and insomnia measurements suggest a potential neuroadaptive mechanism.