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Review
. 2022 Sep 15:16:915995.
doi: 10.3389/fnhum.2022.915995. eCollection 2022.

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

Xinjuan Zhang  1   2 , Jiaxing Zhang  1   2
Affiliations
Review

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

Xinjuan Zhang et al. Front Hum Neurosci. .

Abstract

With the advancement of in vivo magnetic resonance imaging (MRI) technique, more detailed information about the human brain at high altitude (HA) has been revealed. The present review aimed to draw a conclusion regarding changes in the human brain in both unacclimatized and acclimatized states in a natural HA environment. Using multiple advanced analysis methods that based on MRI as well as electroencephalography, the modulations of brain gray and white matter morphology and the electrophysiological mechanisms underlying processing of cognitive activity have been explored in certain extent. The visual, motor and insular cortices are brain regions seen to be consistently affected in both HA immigrants and natives. Current findings regarding cortical electrophysiological and blood dynamic signals may be related to cardiovascular and respiratory regulations, and may clarify the mechanisms underlying some behaviors at HA. In general, in the past 10 years, researches on the brain at HA have gone beyond cognitive tests. Due to the sample size is not large enough, the current findings in HA brain are not very reliable, and thus much more researches are needed. Moreover, the histological and genetic bases of brain structures at HA are also needed to be elucidated.

Keywords: MRI; brain; high altitude; hypoxia; insular cortex; motor cortex; visual cortex.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Diagrammatic drawing of cumulative effects of hypoxia on the brain. (A) Neurons in the brain directly suffer from the stress of low oxygen concentration; (B) cardiovascular and respiratory systems changed in adaptation to hypoxia; (C) through afferent feedback, the adaptation in the cardiovascular and respiratory systems act on their control centers in the brain.
FIGURE 2
FIGURE 2
Schematic diagram shows the brain regions that were affected by HA exposure. The regions include the insular cortex (Zhang et al., 2010, 2013a, 2017; Yan et al., 2011b,d; Fan et al., 2016; Wei et al., 2017; Xin et al., 2020), occipital cortex (Zhang et al., 2010, 2013a, 2017; Yan et al., 2011a,b,c,d; Fan et al., 2016; Zhao et al., 2016; Wang et al., 2017, 2018; Wei et al., 2017; Xin et al., 2020; Xiang et al., 2021), cingulate cortex (Zhang et al., 2010, 2013b; Yan et al., 2011b; Fan et al., 2016; Verges et al., 2016; Chen X. et al., 2017; Wei et al., 2017; Wang et al., 2018), motor cortex (Zhang et al., 2010, 2013a; Chen et al., 2016a; Fan et al., 2016), cerebellum (Yan et al., 2011a; Zhang et al., 2012, 2013a,b; Xin et al., 2020), and hippocampus (Zhang et al., 2013b; Foster et al., 2015; Fan et al., 2016; Chen X. et al., 2017; Xin et al., 2020).
FIGURE 3
FIGURE 3
Changed structure and function in visual cortex in HA population. (A) Increased cortical thickness in sea-level college students who had a 30-day teaching at HA (Fan et al., 2016); (B) increased beta power in soldiers who had garrisoned at HA for 1 month (Zhao et al., 2016); (C) increased amplitude of low-frequency fluctuations (Zhang et al., 2017) (a) and voxel-mirrored homotopic connectivity (Chen et al., 2016b) (b) in soldiers who had garrisoned the frontiers at HA for 2 years; (D) The increased fractional anisotropy in Tibetan adolescents descending to sea level for 4 years (Zhang et al., 2013a); (E) Decreased gray matter volume (Zhang et al., 2010) (a) and decreased cerebrovascular reactivity (Yan et al., 2011b) (b) in the descendants of Han population who have immigrated to HA for several generations; (F) decreased cerebral blood flow (Wang et al., 2018) (a) and cortical thickness (Wei et al., 2017) (b) in HA Tibetan natives; (G) decreased the amplitude of low-frequency fluctuations in college students who studied at HA for 1 year (Wang et al., 2017). The arrow indicates the visual cortex.
FIGURE 4
FIGURE 4
Changed structure and function in insular cortex in HA population. (A) The decreased cortical thickness in sea-level college students who had a 30-day teaching at HA (Fan et al., 2016); (B) hyperintense signaling in a woman after a rapid ascent to mountain (D’Arrigo et al., 2019); (C) the decreased sulcus depth (Wei et al., 2017) (a) and decreased cerebral blood flow (Wang et al., 2018) (b) in HA Tibetan natives; (D) the decreased gray matter volume (Zhang et al., 2010) (a) and longer dwelay of hemodynamic response (Yan et al., 2011b) (b) in the descendants of Han population who have immigrated to HA for several generations; (E) the increased gray matter volume in Tibetan adolescents descending to sea level for 4 years (Zhang et al., 2013a); (F) the decreased ALFF in soldiers who had garrisoned the frontiers at HA for 2 years (Zhang et al., 2017). The arrow indicates the insular cortex.
FIGURE 5
FIGURE 5
Changed structure and function in motor cortex in HA population. (A) The decreased gray matter volume (Zhang et al., 2010) (a) and cerebrovascular reactivity (Yan et al., 2011b) (b) in the descendants of Han population who have immigrated to HA for several generations; (B) the decreased cortical thickness in HA Tibetan natives (Wei et al., 2017); (C) the decreased white matter fiber volume projecting from motor cortex in Everest climbers (Di Paola et al., 2008). (D) the decreased the gray matter volume (Zhang et al., 2013b) (a) and increased regional homogeneity in soldiers who had garrisoned the frontiers at HA for 2 years (Chen et al., 2016a) (b); (E) the increased cortical thickness in sea-level college students who had a 30-day teaching at HA (Fan et al., 2016). The arrow indicates the motor cortex.
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