Resting-State Neuronal Activity and Functional Connectivity Changes in the Visual Cortex after High Altitude Exposure: A Longitudinal Study

Abstract

Damage to the visual cortex structures after high altitude exposure has been well clarified. However, changes in the neuronal activity and functional connectivity (FC) of the visual cortex after hypoxia/reoxygenation remain unclear. Twenty-three sea-level college students, who took part in 30 days of teaching at high altitude (4300 m), underwent routine blood tests, visual behavior tests, and magnetic resonance imaging scans before they went to high altitude (Test 1), 7 days after they returned to sea level (Test 2), as well as 3 months (Test 3) after they returned to sea level. In this study, we investigated the hematological parameters, behavioral data, and spontaneous brain activity. There were significant differences among the tests in hematological parameters and spontaneous brain activity. The hematocrit, hemoglobin concentration, and red blood cell count were significantly increased in Test 2 as compared with Tests 1 and 3. As compared with Test 1, Test 3 increased amplitudes of low-frequency fluctuations (ALFF) in the right calcarine gyrus; Tests 2 and 3 increased ALFF in the right supplementary motor cortex, increased regional homogeneity (ReHo) in the left lingual gyrus, increased the voxel-mirrored homotopic connectivity (VMHC) value in the motor cortex, and decreased FC between the left lingual gyrus and left postcentral gyrus. The color accuracy in the visual task was positively correlated with ALFF and ReHo in Test 2. Hypoxia/reoxygenation increased functional connection between the neurons within the visual cortex and the motor cortex but decreased connection between the visual cortex and motor cortex.

Effects of Long-Term Exposure to 2260 m Altitude on Working Memory and Resting-State Activity in the Prefrontal Cortex: A Large-Sample Cross-Sectional Study

“…Adaptation based on compensatory mechanisms may account for the preserved cognitive performance. In contrast, previous studies showed that the alteration of resting state networks was correlated with the impairment of executive function after two years of exposure to high altitude (3650 m) [ 20 , 21 ]. However, we still do not know the neural adaptive mechanisms of the resting-state brain underlying the long-term exposure to moderate altitude.…”

A longitudinal study on the impact of high‐altitude hypoxia on perceptual processes

“…This face configuration processing stage is significantly affected by hypoxia and recovers slower than the autonomic nervous system. Hypoxia was found to have a longer duration of effect on brain activity than on blood, which might be because the brain consumes the most oxygen and is more sensitive to hypoxia (Zhang et al., 2022). During hypoxia in rats for three weeks, the total area of blood vessels in the brain significantly increases and remains elevated after reoxygenation (Miyamoto et al., 2005).…”

“…Cognitive processes, for example, higher‐order cognitive functions that involve the prefrontal lobe, may employ an adaptive process to compensate for neurocognitive impairment and thus be less affected by hypoxia (Yan et al., 2011). The visual cortex was demonstrated to best reflect the effect and remodeling of hypoxia on the brain (Virués‐Ortega et al., 2004; Zhang et al., 2022) and is critical for the brain to adapt to HA (Chen et al., 2016), making it particularly suitable for monitoring hypoxia adaptation of cognitive processes, which may help us understand how the brain acclimates to harsh environments.…”

“…In previous studies, there has been no consistent conclusion regarding the effects of long‐term and short‐term exposure to HA on visual processing. Several studies suggest that both long‐term and short‐term exposure lead to lateralization of the visual cortex, with the left side requiring more resources for compensation during visual processing (Zhang et al., 2022); however, others have reported that cognitive deficits under long‐term hypoxia are more severe than those under short‐term hypoxia (Sharma et al., 2014; Zhang et al., 2013). In summary, additional empirical research is needed to provide convincing evidence on how prolonged exposure to a moderately high‐altitude environment affects perceptual processes.…”

“…To fill this knowledge gap, the present study adopted a facial S1‐S2 paradigm to evaluate the underlying perceptual processes and electrophysiological mechanisms of lowlanders who sojourned at an altitude and subsequently returned to the lowlands. Based on previous research adopting the same paradigm on two‐year lowlanders exposed to HA (Guo et al., 2021), a longitudinal fMRI (functional magnetic resonance imaging) study of the visual cortex following a similar climbing schedule to that of lowlanders (Zhang et al., 2022) and the potential similarity of changes between the aging process and oxygen deficiency conditions, we anticipated that after approximately four weeks of acclimatization to HA, compared with those at baseline in the lowlands, the heart rate (HR) and diastolic pressure (DBP) would be greater, while the peripheral capillary oxygen saturation (SpO 2 ) would be lower; the N170 amplitude would be significantly greater, and the P1 and N170 latency would be significantly shorter in the HA environment. For the deadaptation process, we speculated that physiological and perceptual processing patterns persist in the HA environment upon return to SL after one week, but after one month, we expected them to return to baseline.…”