Competition among the attentional networks due to resource reduction in Tibetan indigenous residents: evidence from event-related potentials

The effects of long-term high-altitude exposure on cognition: A meta-analysis

Long-term high altitudes (HA) exposure's impact on cognition has yielded inconsistent findings in previous research. To address this, we conducted a meta-analysis of 49 studies (6191 individuals) to comprehensively evaluate this effect. Moderating factors such as cognitive task type, altitude (1500-2500 m, 2500-4000 m, and above 4000 m), residential type (chronic and lifelong), adaptation level and demographic factors were analyzed. Cognitive tasks were classified into eight categories: perceptual processes, psychomotor function, long-term memory, working memory, inhibitory control, problem-solving, language, and others. Results revealed a moderate negative effect of HA on cognitive performance (g = -.40, SE =.18, 95% CI = -.76 to -.05). Psychomotor function and long-term memory notably experience the most pronounced decline, while working memory and language skills show moderate decreases due to HA exposure. However, perceptual processes, inhibitory control, and problem-solving abilities remain unaffected. Moreover, residing at altitudes above 4000 m and being a HA immigrant are associated with significant cognitive impairment. In summary, our findings indicate a selective adaptation of cognitive performance to HA conditions.

The neuroimmune pathway of high-altitude adaptation: influence of erythrocytes on attention networks through inflammation and the autonomic nervous system

Introduction

Many studies have shown that the functional adaptation of immigrants to high-altitude is closely related to oxygen transport, inflammatory response and autonomic nervous system. However, it remains unclear how human attention changes in response to hypoxia-induced neurophysiological activity during high-altitude exposure.

Methods

In the present study, we analyzed the relationship between hypoxic-induced neurophysiological responses and attention networks in 116 immigrants (3,680 m) using an attention network test to simultaneously record electroencephalogram and electrocardiogram in combination with specific routine blood markers.

Results

Our analysis revealed that red blood cells exert an indirect influence on the three attention networks, mediated through inflammatory processes and heart rate variability.

Discussion

The present study provides experimental evidence for the role of a neuroimmune pathway in determining human attention performance at high- altitude. Our findings have implications for understanding the complex interactions between physiological and neurocognitive processes in immigrants adapting to hypoxic environments.

Long-term high-altitude exposure influences task-related representations in visual working memory

Objective

Human working memory is impaired when individuals are exposed to high altitudes, however, whether the capacity of visual working memory is affected remains unclear. This study combined a lateralized change detection task and event-related potentials analysis to explore changes in visual working memory capacity among individuals who emigrated from a low-altitude environment to Tibet (a high-altitude environment).

Materials and methods

Thirty-five college students were recruited from Tibet University as the high-altitude (HA) group, and thirty-six low-altitude (LA) students were enrolled from South China Normal University (sea level) as the LA group. We measured participants' contralateral delay activity (CDA) under different memory loads.

Results

ERP component analysis showed that both the HA and LA groups reached an asymptote at memory load four. However, the contralateral and ipsilateral activity of the HA and LA groups shows different patterns. The results showed a significantly larger contralateral activity for the LA group than for the HA group at memory load one (p = 0.04, Cohen's d = 0.52) and load three (p = 0.02, Cohen's d = 0.61). Additionally, we found marginally larger contralateral activity at memory load four for the LA group (p = 0.06, Cohen's d = 0.47), but not at memory load two (p = 0.10) or load five (p = 0.12). No significant differences were observed for ipsilateral activity. In addition, we observed that the HA group performed larger ipsilateral activity than contralateral activity under each memory load, compared with the LA group.

Conclusion

These findings demonstrated that the attentional resource of long-term HA exposure is more captured by task-irrelevant information, potentially due to impaired inhibitory control, which makes it difficult for them to exclude the interference of task-irrelevant information.

Brain Structural and Functional Alterations in Native Tibetans Living at High Altitude

Tibetans have adapted to high altitude environments. However, the genetic effects in their brains have not been identified. Twenty-five native Tibetans living in Lhasa (3650 m) were recruited for comparison with 20 Han immigrants who originated from lowlands and had been living in Lhasa for two years. The physiological characteristics, brain structure and neuronal spontaneous activity were investigated. Compared with Han immigrants, Tibetans showed higher peripheral oxygen saturation (SpO₂), and lower heart rate, red blood cell counts, hematocrit, and hemoglobin. Tibetans showed increased gray matter volume in the visual cortex, hippocampus, and rectus; increased the amplitudes of low-frequency fluctuations (ALFF) values in the left putamen and left fusiform gyrus; and decreased voxel-mirrored homotopic connectivity (VMHC) values in the precentral gyrus. Moreover, Tibetans have decreased functional connectivity (FC) between the left precentral gyrus and the frontal gyrusand right precuneus. In Tibetans and Han immigrants, hemoglobin and hematocrit were negatively correlated with total gray matter volume in males, SpO₂ was also positively correlated with ALFF in the left fusiform gyrus, while hemoglobin, and hematocrit were positively correlated with VMHC in the precentral gyrus and FC in the precentral gyrus with other brain regions, SpO₂ was also found to be negatively correlated with VMHC in the precentral gyrus, and hemoglobin and hematocrit were negatively correlated with ALFF in the left putamen and left fusiform gyrus. In summary, genetic mutations may result in modulation of some brain regions, which was further confirmed by the identification of correlations with hemoglobin and hematocrit in these regions.

Consistent differences in brain structure and functional connectivity in high-altitude native Tibetans and immigrants

It has been well-established that high-altitude (HA) environments affect the human brain; however, the differences in brain structural and functional networks between HA natives and acclimatized immigrants have not been well clarified. In this study, native HA Tibetans were recruited for comparison with Han immigrants (average of 2.3 ± 0.3 years at HA), with lowland residents recruited as controls. Cortical gray matter volume, thickness, and functional connectivity were investigated using magnetic resonance imaging data. In addition, reaction time and correct score in the visual movement task, hematology, and SpO₂ were measured. In both Tibetans and HA immigrants vs. lowlanders, decreased SpO₂, increased hematocrit and hemoglobin, and increased reaction time and correct score in the visual movement task were detected. In both Tibetans and HA immigrants vs. lowlanders, gray matter volumes and cortical thickness were increased in the left somatosensory and motor cortex, and functional connectivity was decreased in the visual, default mode, subcortical, somatosensory-motor, ventral attention, and subcortical networks. Furthermore, SpO₂ increased, hematocrit and hemoglobin decreased, and gray matter volumes and cortical thickness increased in the visual cortex, left motor cortex, and right auditory cortex in native Tibetans compared to immigrants. Movement time and correct score in task were positively correlated with the thickness of the visual cortex. In conclusion, brain structural and functional network difference in both Tibetan natives and HA immigrants were largely consistent, with native Tibetans only showing more intense brain modulation. Different populations acclimatized to HA develop similar brain mechanisms to cope with hostile HA environmental factors.

Negative relationship between brain-derived neurotrophic factor (BDNF) and attention: A possible elevation in BDNF level among high-altitude migrants

Objective

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophic family that plays a vital role in regulating neuronal activity and synaptic plasticity in the brain, affects attention. However, studies investigating the association between BDNF and attention in long-term high-altitude (HA) migrants are limited in the literature. As HA affects both BDNF and attention, the relationship between these factors becomes more complex. Therefore, this study aimed to evaluate the relationship between peripheral blood concentrations of BDNF and the three attentional networks in both behavioral and electrical aspects of the brain in long-term HA migrants.

Materials and methods

Ninety-eight Han adults (mean age: 34.74 ± 3.48 years, 51 females and 47 males, all have lived at Lhasa for 11.30 ± 3.82 years) were recruited in this study. For all participants, the serum BDNF levels were assessed using enzyme-linked immunosorbent assay; event-related potentials (N1, P1, and P3) were recorded during the Attentional Networks Test, which was used as the measure of three attentional networks.

Results

Executive control scores were negatively correlated with P3 amplitude (r = -0.20, p = 0.044), and serum BDNF levels were positively correlated with executive control scores (r = 0.24, p = 0.019) and negatively correlated with P3 amplitude (r = -0.22, p = 0.027). Through grouping of BDNF levels and three attentional networks, executive control was found to be significantly higher in the high BDNF group than in the low BDNF group (p = 0.010). Different BDNF levels were associated with both orienting scores (χ² = 6.99, p = 0.030) and executive control scores (χ² = 9.03, p = 0.011). The higher the BDNF level, the worse was the executive function and the lower was the average P3 amplitude and vice versa. Females were found to have higher alerting scores than males (p = 0.023).

Conclusion

This study presented the relationship between BDNF and attention under HA. The higher the BDNF level, the worse was the executive control, suggesting that after long-term exposure to HA, hypoxia injury of the brain may occur in individuals with relatively higher BDNF levels, and this higher BDNF level may be the result of self-rehabilitation tackling the adverse effects brought by the HA environment.

Intermittent hypoxic conditioning restores neurological dysfunction of mice induced by long-term hypoxia

BACKGROUND

Central nervous system diseases are associated with hypoxia, which usually cause irreversible nerve damage, but the underlying mechanism is unclear and effective intervention strategies are lacking. This study was designed to explore the mechanism and treatment strategy of hypoxia-induced nerve injury.

METHODS

In this study, 13% O₂ was used to treat mice for 0, 1, 3 7, and 14 days, Morris water maze and other animal behavior experiments were used to evaluate the neurological function of mice. TUNEL, BrdU, PCNA, DCX, and SOX2 staining were used to observe the apoptosis and proliferation of mouse neurons. RT-PCR and Iba1 staining were used to evaluate the release of inflammatory factors IL-1β, IL-6, and TNF-α and the activation of microglia.

RESULTS

Short-term hypoxia promotes neurogenesis, while long-term hypoxia inhibits neurogenesis. The changes in hypoxia-induced neurogenesis were positively correlated with neurological functions, but negatively correlated with apoptosis. Moreover, intermittent hypoxic conditioning restored long-term hypoxia-induced neurological dysfunction by promoting neural stem cell generation and inhibiting the release of inflammatory factors IL-1β, IL-6, and TNF-α and the activation of microglia.

CONCLUSION

Hypoxia promoted neurogenesis in a time-dependent manner, and intermittent hypoxic conditioning exerted a neuroprotective effect through promoting neural stem cell generation and suppressing inflammation induced by long-term hypoxia stress, which provided a novel concept to develop a treatment for hypoxia-related brain injury.

Disrupted gut microbiota aggravates working memory dysfunction induced by high-altitude exposure in mice

BACKGROUND

The widely accepted microbiome-gut-brain axis (MGBA) hypothesis may be essential for explaining the impact of high-altitude exposure on the human body, especially brain function. However, studies on this topic are limited, and the underlying mechanism remains unclear. Therefore, this study aimed to determine whether high-altitude-induced working memory dysfunction could be exacerbated with gut microbiota disruption.

METHODS AND RESULTS

C57BL/6 mice were randomly divided into three groups: control, high-altitude exposed (HAE), and high-altitude exposed with antibiotic treatment (HAE-A). The HAE and HAE-A groups were exposed to a low-pressure oxygen chamber (60-65 kPa) simulating the altitude of 3,500-4,000 m for 14 days, The air pressure level for the control group was maintained at 94.5 kPa. Antibiotic water (mixed with 0.2 g/L of ciprofloxacin and 1 g/L of metronidazole) was provided to the HAE-A group. Based on the results of the novel object test and P300 in the oddball behavioral paradigm training test, working memory dysfunction was aggravated by antibiotic treatment. We determined the antioxidant capacity in the prefrontal cortex and found a significant negative influence (p < 0.05) of disturbed gut microbiota on the total antioxidant capacity (T-AOC) and malondialdehyde (MDA) content, as well as the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). The same trend was also observed in the apoptosis-related functional protein content and mRNA expression levels in the prefrontal cortex, especially the levels of bcl-2, Bax, and caspase-3. The high-altitude environment and antibiotic treatment substantially affected the richness and diversity of the colonic microbiota and reorganized the composition and structure of the microbial community. S24-7, Lachnospiraceae, and Lactobacillaceae were the three microbial taxa with the most pronounced differences under the stimulation by external factors in this study. In addition, correlation analysis between colonic microbiota and cognitive function in mice demonstrated that Helicobacteraceae may be closely related to behavioral results.

CONCLUSION

Disrupted gut microbiota could aggravate working memory dysfunction induced by high-altitude exposure in mice, indicating the existence of a link between high-altitude exposure and MGBA.

Attention Network Changes of High-Altitude Migrants

INTRODUCTION: The present study aimed to explore whether there are changes in the alerting, orienting, and executive network efficiencies of attention function between high altitude immigrants and low altitude residents.METHODS: Event-related potentials (ERP) were acquired during an attention network test (ANT). The high-altitude (HA) group comprised 22 college student immigrants who were born and raised at low altitudes and had lived at a HA (11,975 ft/3650 m) for 26 mo (tests were conducted when they returned to HA for 3 mo). The low-altitude (LA) group comprised 23 college students who had never visited HA areas before.RESULTS: Compared with the LA group, the HA group had a higher pulse rate, lower oxygen saturation level, and decreased alerting and orienting effects in the behavioral results. The ERP results of the HA group showed a smaller P1 in the occipital area, a larger N1 both in the parietal and occipital areas of the alerting network, and a smaller P1 and larger N1 in the orienting network than the LA group. In the executive control network, the N2 amplitude of the HA group was more negative and the P3 amplitude of the HA group decreased in incongruent conditions.DISCUSSION: Together, these findings suggest that high-altitude migrants are less effective at alerting and orienting than low-altitude residents. For executive control function, changes in the P3 amplitudes of incongruent conditions indicated a decrease in conflict inhibition underlying the executive-control network.An X, Tao G, Zhang X, Ma H, Wang Y. Attention network changes of high-altitude migrants. Aerosp Med Hum Perform. 2022; 93(11):791–799.

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

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.

Changes in Hippocampus and Amygdala Volume with Hypoxic Stress Related to Cardiorespiratory Fitness under a High-Altitude Environment

The morphology of the hippocampus and amygdala can be significantly affected by a long-term hypoxia-induced inflammatory response. Cardiorespiratory fitness (CRF) has a significant effect on the neuroplasticity of the hippocampus and amygdala by countering inflammation. However, the role of CRF is still largely unclear at high altitudes. Here, we investigated brain limbic volumes in participants who had experienced long-term hypoxia exposure in Tibet (3680 m), utilizing high-resolution structural images to allow the segmentation of the hippocampus and amygdala into their constituent substructures. We recruited a total of 48 participants (48 males; aged = 20.92 ± 1.03 years) to undergo a structural 3T MRI, and the levels of maximal oxygen uptake (VO_2max) were measured using a cardiorespiratory function test. Inflammatory biomarkers were also collected. The participants were divided into two groups according to the levels of median VO_2max, and the analysis showed that the morphological indexes of subfields of the hippocampus and amygdala of the lower CRF group were decreased when compared with the higher CRF group. Furthermore, the multiple linear regression analysis showed that there was a higher association with inflammatory factors in the lower CRF group than that in the higher CRF group. This study suggested a significant association of CRF with hippocampus and amygdala volume, which may be related to hypoxic stress in high-altitude environments. A better CRF reduced physiological stress and a decrease in the inflammatory response was observed, which may be related to the increased oxygen transport capacity of the body.

Research on drivers' hazard perception in plateau environment based on visual characteristics

A good visual search mode is an important prerequisite for a driver to perceive the hazard in the traffic environment timely and accurately. However, hypoxia conditions in the plateau environment might affect drivers' cognitive and judgment ability, posing potential threats to safe driving. This study analyzed the eye movement behaviors of drivers when faced with traffic hazards in the plateau environment, to examine the impact level of altitude on drivers' perception and reaction. Nine typical traffic hazard scenarios were investigated at four locations with four different altitudes, including Linzhi, Lhasa, Naqu, and Yanghu Scenic Area based on UC-WIN / ROAD driving simulation software. Then, drivers' visual search modes were analyzed according to drivers' eye movement data collected by ASL Mobile Eye monocular eye tracker. As the altitude increased, the drivers' first fixation time and the average saccade amplitude decreased, while the fixation duration percentage increased. Drivers with fewer years of driving experience had a larger percentage of fixation duration and a smaller saccade amplitude. In addition, a shorter acclimation period also negatively influenced the percentage of fixation time. The increase of altitude would weaken the drivers' visual sensitivity and cognitive processing ability of hazard information, which would reduce drivers' hazard perception skills, and the increase of driving experience might help alleviate such negative impacts to some extent. Based on the visual characteristics of traffic hazard scenarios obtained in this paper, the training of highly accident-prone drivers can be guided specifically to improve their visual search strategies, thereby improving driving safety.

Alteration of Behavioral Inhibitory Control in High-Altitude Immigrants

Behavioral inhibitory control (BIC) acts as a key cognitive ability, which is essential for humans to withhold inappropriate behaviors. Meanwhile, many studies reported that long-term exposure to high altitude (HA) may affect cognitive ability. However, it is not clear whether long-term exposure to HAs may affect the BIC of an individual. To clarify the role of altitude in the behavioral control of adults and the underlying neural mechanism, we explored the BIC neural activity profiles of healthy immigrants from low-altitude (LA) regions to HA regions. Combining a two-choice oddball paradigm and electrophysiological techniques, this study monitored the N2 and P3 event-related components and neural oscillations across LA and HA groups. Results showed longer reaction times (RTs) for the HA group than the LA group. Relative to the LA group, lower N2 and P3 amplitudes were observed for the HA group. Significant positive correlations were also found between P3 amplitude and theta/delta band power across both groups. Importantly, lower theta/delta band powers were only observed for the HA group under the deviant condition. Collectively, these findings suggest that long-term exposure to HAs may attenuate BIC during the response inhibition stage and provide valuable insights into the neurocognitive implications of environmental altitude on BIC.

Altered Attention Network in Paratroopers Exposed to Repetitive Subconcussion: Evidence Based on Behavioral and Event-Related Potential Results

Cognitive impairment caused by repetitive subconcussion has received increasing attention in recent years. Although the dysfunction of attention has been confirmed by neuropsychological research using scales, there is no event-related potentials (ERPs) research. The Attention Network Test (ANT) has been widely used to evaluate the three separate components of attention processing (alerting, orienting, and executive control). Twenty-seven paratroopers exposed to repetitive subconcussion (subconcussion group) and 25 matched healthy control participants (HCs group) were enrolled, and all of them performed the ANT test while continuous scalp electroencephalography data were recorded. On the behavioral performance level, the subconcussion group showed a slower task response, with an especially significant slower reaction time in alerting. Concerning ERP results, reduction amplitudes of cue-N1 in the alerting network were observed, indicating that this group was less able to make efficient use of cues and maintain an alerting state for incoming information. For the orienting network, no difference in N1 amplitude was observed between the two groups. Moreover, there was a reduced P3 amplitude in the executive control network in the subconcussion group compared with the HCs group, suggesting a dysfunction of attentional resource allocation and inhibition control in the former group. This study is, to our knowledge, the first analysis of the altered attention network caused by repetitive subconcussion from the perspectives of behavioral and neuropsychology levels. These preliminary results revealed the possible damage of the alerting and executive control networks and provided a reference for further research on subconcussion cognitive impairment.

Electrophysiological mechanisms underlying hypoxia-induced deficits in visual spatial and non-spatial discrimination

Impaired visual cognition in residents of hypoxic environment has been widely reported; however, the underlying electrophysiological mechanisms remain unclear. In this study, 23 college students underwent three sessions of a Clock task test before a 30-day high-altitude exposure (Test 1) and 1 week (Test 2) and 3 months (Test 3) after they returned to lowlands. The Clock task consists of a visual spatial angle and a visual non-spatial color discrimination subtask. Simultaneously, electroencephalography (EEG) was recorded during the Clock task. The behavioral results showed that, compared with Test 1, accuracy in Test 2 was significantly decreased in both the Angle and Color tasks, and reaction time (RT) was significantly increased in the Angle task. The event-related potentials results showed that, during both tasks amplitudes of the occipital N1 and P3 components during both tasks were significantly decreased in Test 2, compared with Test 1. Moreover, N1 amplitude was negatively correlated with RT and positively correlated with accuracy. Further time-frequency EEG analysis showed that theta power at occipital sites was significantly decreased in both tasks in Test 2, compared with Test 1, and was negatively correlated with RT in the Angle task. In Test 3, both the behavioral performance and EEG activity recovered to the baseline level in Test 1. These findings suggested that hypoxia impairs both visual spatial and visual non-spatial discriminations, and these impairments can recover after subjects return to lowlands. Inhibition of brain electrophysiological activity in the visual cortex may explain the deficits in visual cognition.

Decreased Event-Related Desynchronization of Mental Rotation Tasks in Young Tibetan Immigrants

The present study aimed to explore the cortical activity underlying mental rotation in high-altitude immigrants via the event-related desynchronization (ERD), the electroencephalogram time–frequency analysis, and source localization based on electroencephalographic data. When compared with the low-altitude individuals, the reaction time of mental rotation tasks was significantly slower in immigrants who had lived in high-altitude areas for 3 years. The time–frequency analysis showed that the alpha ERD and the beta ERD within the time window (400–700 ms) were decreased during the mental rotation tasks in these immigrants. The decreased ERD was observed at the parietal–occipital regions within the alpha band and at the central–parietal regions within the beta band. The decreased ERD might embody the sensorimotor-related cortical activity from hypoxia, which might be involved in cognitive control function in high-altitude immigrants, which provided insights into the neural mechanism of spatial cognition change on aspect of embodied cognition due to high-altitude exposure.

Different neurocognitive patterns of conflict control in Tibetans living above and below 4,000 m

Background

The existence of a particular threshold of hypoxia severity, beyond which neuropsychological functioning is compromised, is unclear. We investigated the neurocognitive profile related to conflict control in healthy young Tibetans born and living at three different altitudes (2,700 m, 3,700 m, and 4,500 m) in Tibet to investigate the existence of this threshold.

Methods

Using event-related potentials (ERPs), the conflict control functions of individuals in the three altitude groups were investigated by means of a flanker task, using congruent and incongruent stimuli. The data were analyzed using mixed-model analyses of variance.

Results

Although effect of altitude was not significant at a behavioral level (p > 0.05), the ERPs showed cognitive conflict modulation. The N2 difference wave (for incongruent minus congruent conditions) was smaller in the 4,500-m group than in the groups living below 4,000 m (p < 0.05). The study’s findings suggest that the influence of high altitude in the conflict monitoring stage becomes significant above 4,000 m. Thus, the altitude threshold for impairment of cognition may be 4,000 m.