Combined fractional anisotropy and subcortical volumetric abnormalities in healthy immigrants to high altitude: A longitudinal study

Abstract

The study of individuals at high‐altitude (HA) exposure provides an important opportunity for unraveling physiological and psychological mechanism of brain underlying hypoxia condition. However, this has rarely been assessed longitudinally. We aim to explore the cognitive and cerebral microstructural alterations after chronic HA exposure. We recruited 49 college freshmen who immigrated to Tibet and followed up for 2 years. Control group consisted of 49 gender and age‐matched subjects from sea level. Neuropsychological tests were also conducted to determine whether the subjects' cognitive function had changed in response to chronic HA exposure. Surface‐based cortical and subcortical volumes were calculated from structural magnetic resonance imaging data, and tract‐based spatial statistics (TBSS) analysis of white matter (WM) fractional anisotropy (FA) based on diffusion weighted images were performed. Compared to healthy controls, the high‐altitude exposed individuals showed significantly lower accuracy and longer reaction times in memory tests. Significantly decreased gray matter volume in the caudate region and significant FA changes in multiple WM tracts were observed for HA immigrants. Furthermore, differences in subcortical volume and WM integration were found to be significantly correlated with the cognitive changes after 2 years' HA exposure. Cognitive functions such as working memory and psychomotor function were found to be impaired during chronic HA. Differences of brain subcortical volumes and WM integration between HA and sea‐level participants indicated potential impairments in the brain structural modifications and microstructural integrity of WM tracts after HA exposure.

Chronic Exposure to Hypoxia Inhibits Myelinogenesis and Causes Motor Coordination Deficits in Adult Mice

“…It remains unclear how hypoxia causes functional deficits in adult mice. White matter abnormalities have been reported in OSA and CMS patients [8,[43][44][45][46]. As an important component of the CNS, myelin is highly enriched in the white matter and abundant in the gray matter.…”

The human brain in a high altitude natural environment: A review

“…Regional GM changes were seen in the mountain climbers who repeated expeditions to Mount Everest ( Di Paola et al, 2008 ), adult soldiers who had garrisoned the frontiers in the Qinghai-Tibet Plateau for 2 years ( Zhang et al, 2013b ), climbers who made a single ascent to for less than 36 h ( D’Arrigo et al, 2019 ), and college freshmen who immigrated to the Qinghai-Tibet Plateau and were followed-up for 2 years ( Chen X. et al, 2017 , Chen et al, 2019a ). To explore the influences of the environment on HA residents, Han immigrant adolescents ( Zhang et al, 2010 ) and HA adolescents ( Yan et al, 2010 ; Wei et al, 2017 ) living in the Qinghai-Tibet Plateau were studied, and decreased GM volume and changes in cortical thickness were detected.…”

“…Moreover, the number of commissural fibers connecting the bilateral visual cortices increased in adults who had immigrated to and remained on a plateau for 2 years ( Chen et al, 2016b ). Changes of FA of WM fibers were observed in a lot of studies on descendants of Han immigrants ( Zhang et al, 2010 ), Tang-ku-la Mountains climbers ( Zhang et al, 2012 ), soldiers who have garrisoned the frontiers in Qinghai-Tibet Plateau ( Zhang et al, 2013b ), subjects as volunteer teachers ( Fan et al, 2016 ), and college freshmen who immigrated to Tibet and followed up for 2 years ( Chen et al, 2019a ), with some fibers have increased FA but others have decreased FA ( Table 1 ).…”

Cognitive impairment caused by hypoxia: from clinical evidences to molecular mechanisms

“…Moreover, atrophy of the caudate and subcortex was observed on MRI. The injury was irreversible, and longer exposure lead to more severe injuries (Chen et al 2019). In addition, compared to those living at sea level, the migrators with 1-5 years of high altitude residence exhibited impaired learning ability (Abraini et al 1998), color attention, visual memory, and complex cognitive ability (Bouquet et al 1999) (Gao et al 2015;Yan et al 2011).…”