Effects of Chronic Hypoxic Environment on Cognitive Function and Neuroimaging Measures in a High-Altitude Population

Abstract

ObjectiveThis study aimed to investigate the effects of long-term hypoxic environment exposure on cognitive ability and neuroimaging characteristics in a highland population in China.MethodsHealth system workers in Maduo County (4,300 m above sea level) and Minhe County (1,700 m above sea level) were selected as research participants and divided into a high-altitude (HA) group and low-altitude (LA) group, respectively. Cognitive ability was assessed using the Montreal Cognitive Assessment (MoCA), Verbal Fluency Test (VFT), Symbol Digit Modalities Test (SDMT), Trail Making Test A and B (TMT), Digit Span Test (DST), and Rey Auditory Verbal Learning Test (RAVLT). All participants underwent a magnetic resonance imaging (MRI) scan, resting state functional MRI scan, and diffusion tensor imaging to clarify changes in regional gray matter (GM) volume, anisotropy index (FA), local consistency (ReHo), and low-frequency oscillation amplitude (ALFF).ResultsThe HA group had significantly lower MoCA, DST, VFT, RAVLT, and TMT scores compared to the control group. No significant differences were found in SDMT score. Furthermore, compared to the LA group, the HA group had significantly lower GM density of the left olfactory cortex, right medial orbital superior frontal gyrus, bilateral insula, left globus pallidus, and temporal lobe (left superior temporal gyrus temporal pole, bilateral middle temporal gyrus temporal pole, and right middle temporal gyrus). In terms of FA, compared with the LA group, the HA group had lower values for the corpus callosum, corpus callosum knee, bilateral radiative corona, and left internal capsule. The HA group had lower ALFF values of the left cerebellum, left putamen, left orbital inferior frontal gyrus, and left precuneus, but higher ALFF values of the left fusiform gyrus, bilateral inferior temporal gyrus, left orbital superior frontal gyrus and medial superior frontal gyrus, compared to the LA group. There was no significant group difference in ReHo values.ConclusionOur findings suggest that a chronic hypoxic environment can induce extensive cognitive impairment. Decreased GM density in multiple brain regions, damaged nerve fibers, and unbalanced neuronal activity intensity in different brain regions may be the structural and functional basis of cognitive impairment due to hypoxia.

Olfactory functional covariance connectivity in Parkinson’s disease: Evidence from a Chinese population

“…They found that the ALFF was reduced in the left cerebellum, right anterior cuneiform lobe, and left posterior central/supramarginal gyrus (PostC) in patients with PD, and a greater decrease in the ALFF was observed in the left pallidum and anterior central gyrus/PostC, and the left caudate nucleus/putamen showed a positive correlation with the disease course, similar to some results of the current study. Zhang et al (2022) found that chronic hypoxia can lead to extensive cognitive impairment, in addition to a significant reduction in the ROI density of the left olfactory cortex, right medial superior orbitofrontal gyrus, bilateral insular lobes, left globus pallidus and temporal lobe. These findings also support the idea that changes in orbitofrontal gyrus brain function may be a promising imaging marker in Parkinson’s disease, consistent with our idea.…”

Effects of long-term exposure to high altitude on brain structure in healthy people: an MRI-based systematic review and meta-analysis

“…Another study by the same team found that Tibetans who lived at high altitudes for a long time had increased GM volume in the visual cortex, hippocampus and rectus (36). Another study showed that the GM volume in HA residents is significantly higher than LA residents in the bilateral somatosensory cortex and vision cortex (37) superior frontal gyrus, bilateral insula, left globus pallidus, and temporal lobe (28). Feng et al's observation of healthy people who migrated to Lhasa (3,658 m) for 2 years, showed that no significant change in total GM volume compared with the SL group, but there were decreased regional GM volume in the HA group, such as putamen, insula, amygdala, pale nucleus, hippocampus, amygdala (40).…”

“…In terms of ReHo analysis, the included studies produced inconsistent results. Zhang et al found no significant difference in ReHo values between highaltitude HA group and LA group (28,36). However, Chen et al reported ReHo increased significantly in bilateral hippocampus, and decreased significantly in bilateral putamen, bilateral superior temporal gyrus, and medial frontal gyrus, after prolonged exposure to high-altitude (42).…”

“…Cohort studies with the total number of 13 studies were assessed via the Newcastle-Ottawa Scale (NOS). Eight studies had NOS scores of 6 (20,(28)(29)(30)(31)(32)(33)(34), and 5 studies scored 5 (35)(36)(37)(38)(39). The overall quality of included studies was at a medium level, with a mean NOS score of 5.62 (Table 1).…”

“…This systematic review included 16 observational studies, published between 2010 and 2023, and the main characteristics of the included studies are shown in Table 2. Thirteen of the 16 studies were cohort studies (20,(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39), and one was a cross-sectional study (40), and two longitudinal studies (41,42). Some of these studies were observations of different MRI outcomes in the same population [(41, 42) were the same population; (20,30,31,38) were the same population; (33,39) were the same population].…”