The effect of jet lag on the human brain: A neuroimaging study

Stress Response to Winter Warfare Training: Potential Impact of Location

INTRODUCTION

Winter warfare training (WWT) is a critical component of military training that trains warfighters to operate effectively in extreme environments impacted by snow and mountainous terrain. These environmental factors can exacerbate the disruption to the hormone milieu associated with operating in multi-stressor settings. To date, there is limited research on the physiological responses and adaptations that occur in elite military populations training in arduous environments. The purpose of this study was to quantify hormone responses and adaptations in operators throughout WWT.

MATERIALS AND METHODS

Participants engaged in baseline laboratory metrics at their home station, Fort Carson, located in Colorado (CO) prior to WWT, for one week in Montana (MT) and one week in Alaska (AK). WWT periods were separated by approximately one month. Blood was collected upon wake at baseline (CO) and on the first and last day of WWT at each location (MT and AK). Plasma was analyzed for stress, metabolic, and growth-related hormones via enzyme-linked immunoassay (ELISA). Sleep quality was assessed via the Pittsburg Sleep Quality Index (PSQI) at baseline (CO) and on the first day of training in MT and AK. Cognitive function was evaluated using the Defense Automated Neurobehavioral Assessment (DANA) at baseline (CO) and on the first and last day of WWT in both MT and AK.

RESULTS

Fourteen US Army operators in 10th Special Forces Group (SFG) Operational Detachment participated in winter warfare training (WWT; age: 31.5 years; 95%CI[28.1, 34.3]; height: 180.6 cm; 95%CI[177.3, 183.4]; weight: 87.4 kg.; 95%CI[80.6, 97.7]; body fat: 18.9%; 95%CI[13.7, 23.1]; male: n=13; female: n=1). Plasma adrenocorticotropic hormone (ACTH) levels increased from baseline (19.9 pg/mL; 95%CI[8.6, 24.2])  to pre-WWT (26.9 pg/mL; 95%CI [16.2, 37]; p=0.004), decreased from pre-  (26.9 pg/mL; 95%CI [16.2, 37]) to post-WWT in MT (22.3 pg/mL; 95% CI [8, 23.7]; p=0.004;), and increased from pre-  (25 pg/mL; 95%CI[ 28.4) to post-WWT (36.6 pg/mL; 95%CI [17.9, 48.9]) in AK (p=0.005). Plasma cortisol levels decreased from pre- (174 ng/mL; 95%CI[106.2, 233.6])  to post-WWT (94.5 ng/mL; 95%CI[54.8, 101.7]) in MT (p=0.001) and, conversely, increased from pre- (123.1 ng/mL; 95%CI[97.5, 143.9]) to post-WWT  (162.8 ng/mL; 95%CI[128, 216.7]) in AK (p<0.001). Alterations in growth-related hormones (insulin-like growth factor 1 [IGF-1], insulin-like growth factor binding protein 3 [IGFBP-3],  and sex hormone binding globulin [SHBG]) were observed throughout WWT (p<0.05). The Total Testosterone / Cortisol ratio (TT / CORT; molar ratio) was lower pre-WWT in MT (0.04; 95%CI[0.01,0.04) compared to baseline in CO (0.07; 95%CI[0.04, 0.07]; p=0.042). Triiodothyronine (T3) levels increased from pre-  (101.7 ng/dL; 95%CI[93.7, 110.4]) to post-WWT  (117.8 ng/dL; 95%CI[105.1, 129.4]) in MT (p=0.042). No differences in sleep quality were reported between locations (CO, MT, and AK). Alterations in cognitive function were exhibited between locations and during WWT in both MT and AK (p<0.05).

CONCLUSIONS

Over the course of WWT, elite operators experienced alterations in stress, metabolic, and growth-related hormones, as well as cognitive performance. The increase in stress hormones (i.e., ACTH and cortisol) and reduction in cognitive performance following training in AK are suggestive of heightened physiological strain, despite similarities in physical workload, self-reported sleep quality, and access to nutrition. The variation in hormone levels documented between MT and AK may stem from differences in environmental factors, such as lower temperatures and harsh terrain. Further research is warranted to provide more information on the combined effects of military training in extreme environments on operator health and performance.

Decoupling of gray and white matter functional networks in cognitive impairment induced by occupational aluminum exposure

Aluminum (Al) is a low-toxic, accumulative substance with neurotoxicity properties that adversely affect human cognitive function. This study aimed to investigate the neurobiological mechanisms underlying cognitive impairment resulting from occupational Al exposure. Resting-state functional magnetic resonance imaging was conducted on 54 individuals with over 10 years of Al exposure. Al levels were measured, and cognitive function was assessed using the Montreal Cognitive Assessment (MoCA). Subsequently, the K-means clustering algorithm was employed to identify functional gray matter (GM) and white matter (WM) networks. Two-sample t-tests were conducted between the cognition impairment group and the control group. Al exhibited a negative correlation with MoCA scores. Participants with cognitive impairment demonstrated reduced functional connectivity (FC) between the middle cingulum network (WM1) and anterior cingulum network (WM2), as well as between the executive control network (WM6) and limbic network (WM10). Notably, decreased FCs were observed between the executive control network (GM5) and WM1, WM4, WM6, and WM10. Additionally, the FC of GM5-GM4 and WM1-WM2 negatively correlated with Trail Making Test Part A (TMT-A) scores. Prolonged Al accumulation detrimentally affects cognition, primarily attributable to executive control and limbic network disruptions.

Chronic phase advances reduces recognition memory and increases vascular cognitive dementia-like impairments in aged mice

Disrupted or atypical light-dark cycles disrupts synchronization of endogenous circadian clocks to the external environment; extensive circadian rhythm desynchrony promotes adverse health outcomes. Previous studies suggest that disrupted circadian rhythms promote neuroinflammation and neuronal damage post-ischemia in otherwise healthy mice, however, few studies to date have evaluated these health risks with aging. Because most strokes occur in aged individuals, we sought to identify whether, in addition to being a risk factor for poor ischemic outcome, circadian rhythm disruption can increase risk for vascular cognitive impairment and dementia (VCID). We hypothesized that repeated 6 h phase advances (chronic jet lag; CJL) for 8 weeks alters cerebrovascular architecture leading to increased cognitive impairments in aged mice. Female CJL mice displayed impaired spatial processing during a spontaneous alternation task and reduced acquisition during auditory-cued associative learning. Male CJL mice displayed impaired retention of the auditory-cued associative learning task 24 h following acquisition. CJL increased vascular tortuosity in the isocortex, associated with increased risk for vascular disease. These results demonstrate that CJL increased sex-specific cognitive impairments coinciding with structural changes to vasculature in the brain. We highlight that CJL may accelerate aged-related functional decline and could be a crucial target against disease progression.

Consensus Recommendations for Standardized Data Elements, Scales, and Time Segmentations in Studies of Human Circadian/Diurnal Biology and Stroke

Increasing evidence indicates that circadian and diurnal rhythms robustly influence stroke onset, mechanism, progression, recovery, and response to therapy in human patients. Pioneering initial investigations yielded important insights but were often single-center series, used basic imaging approaches, and used conflicting definitions of key data elements, including what constitutes daytime versus nighttime. Contemporary methodologic advances in human neurovascular investigation have the potential to substantially increase understanding, including the use of large multicenter and national data registries, detailed clinical trial data sets, analysis guided by individual patient chronotype, and multimodal computed tomographic and magnetic resonance imaging. To fully harness the power of these approaches to enhance pathophysiologic knowledge, an important foundational step is to develop standardized definitions and coding guides for data collection, permitting rapid aggregation of data acquired in different studies, and ensuring a common framework for analysis. To meet this need, the Leducq Consortium International pour la Recherche Circadienne sur l'AVC (CIRCA) convened a Consensus Statement Working Group of leading international researchers in cerebrovascular and circadian/diurnal biology. Using an iterative, mixed-methods process, the working group developed 79 data standards, including 48 common data elements (23 new and 25 modified/unmodified from existing common data elements), 14 intervals for time-anchored analyses of different granularity, and 7 formal, validated scales. This portfolio of standardized data structures is now available to assist researchers in the design, implementation, aggregation, and interpretation of clinical, imaging, and population research related to the influence of human circadian/diurnal biology upon ischemic and hemorrhagic stroke.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

[Correlation of the Karolinska sleepiness scale with performance variables of the monotonous bimanual psychomotor test]

OBJECTIVE

To assess the objectivity of measuring the level of sleepiness in the subjects using a monotonous psychomotor bimanual tapping test developed by us, performed on mobile devices running Android OS.

MATERIAL AND METHODS

Four hundred and ninety-four hour-long experiments with the performance of a psychomotor test were conducted on 102 students. Using the method of mixed linear models, correlations between the levels of sleepiness according to the Karolinska Sleepiness Scale (KSS) and the Epworth Sleepiness Scale (ESS) and the behavioral indicators of the test were evaluated.

RESULTS

Statistically significant correlations between the increase in KSS scores and such indicators as a decrease in the total number of button taps and an increase in the frequency of «microsleep» episodes are shown. Statistically significant correlations of ESS score characteristics with the behavioral indicators of the test were not found.

CONCLUSION

A large statistical material shows a reliable correlation of the parameters of the psychomotor test with the level of sleepiness on the Karolinska scale, which allows using the mobile application developed by us to determine the current level of sleepiness /alertness in the field.

Effects of exogenous melatonin on sleep and circadian rhythms in women with premenstrual dysphoric disorder

We previously found normal polysomnographic (PSG) sleep efficiency, increased slow-wave sleep (SWS), and a blunted melatonin secretion in women with premenstrual dysphoric disorder (PMDD) compared to controls. Here, we investigated the effects of exogenous melatonin in five patients previously studied. They took 2 mg of slow-release melatonin 1 h before bedtime during their luteal phase (LP) for three menstrual cycles. At baseline, patients spent every third night throughout one menstrual cycle sleeping in the laboratory. Measures included morning urinary 6-sulfatoxymelatonin (aMt6), PSG sleep, nocturnal core body temperature (CBT), visual analog scale for mood (VAS-Mood), Prospective Record of the Impact and Severity of Menstrual Symptoms (PRISM), and ovarian plasma hormones. Participants also underwent two 24-hour intensive physiological monitoring (during the follicular phase and LP) in time-isolation/constant conditions to determine 24-hour plasma melatonin and CBT rhythms. The same measures were repeated during their third menstrual cycle of melatonin administration. In the intervention condition compared to baseline, we found increased urinary aMt6 (p < 0.001), reduced objective sleep onset latency (p = 0.01), reduced SWS (p < 0.001), and increased Stage 2 sleep (p < 0.001). Increased urinary aMt6 was correlated with reduced SWS (r = -0.51, p < 0.001). Circadian parameters derived from 24-hour plasma melatonin and CBT did not differ between conditions, except for an increased melatonin mesor in the intervention condition (p = 0.01). Ovarian hormones were comparable between the conditions (p ≥ 0.28). Symptoms improved in the intervention condition, as measured by the VAS-Mood (p = 0.02) and the PRISM (p < 0.001). These findings support a role for disturbed melatonergic system in PMDD that can be partially corrected by exogenous melatonin.

Effect of jet lag on brain white matter functional connectivity

Background

A long-haul flight across more than five time zones may produce a circadian rhythm sleep disorder known as jet lag. Little is known about the effect of jet lag on white matter (WM) functional connectivity (FC).

Objective

The present study is to investigate changes in WM FC in subjects due to recovery from jet lag after flying across six time zones.

Methods

Here, resting-state functional magnetic resonance imaging was performed in 23 participants within 24 hours of flying and again 50 days later. Gray matter (GM) and WM networks were identified by k-means clustering. WM FC and functional covariance connectivity (FCC) were analyzed. Next, a sliding window method was used to establish dynamic WM FC. WM static and dynamic FC and FCC were compared between when participants had initially completed their journey and 50 days later. Emotion was assessed using the Positive and Negative Affect Schedule and the State Anxiety Inventory.

Results

All participants were confirmed to have jet lag symptoms by the Columbian Jet Lag Scale. The static FC strengthes of cingulate network (WM7)- sensorimotor network and ventral frontal network- visual network were lower after the long-haul flight compared with recovery. Corresponding results were obtained for the dynamic FC analysis. The analysis of FCC revealed weakened connections between the WM7 and several other brain networks, especially the precentral/postcentral network. Moreover, a negative correlation was found between emotion scores and the FC between the WM7 and sensorimotor related regions.

Conclusions

The results of this study provide further evidence for the existence of WM networks and show that jet lag is associated with alterations in static and dynamic WM FC and FCC, especially in sensorimotor networks. Jet lag is a complex problem that not only is related to sleep rhythm but also influences emotion.

Mammalian circadian systems: Organization and modern life challenges

Humans and other mammalian species possess an endogenous circadian clock system that has evolved in adaptation to periodically reoccurring environmental changes and drives rhythmic biological functions, as well as behavioural outputs with an approximately 24-hour period. In mammals, body clocks are hierarchically organized, encompassing a so-called pacemaker clock in the hypothalamic suprachiasmatic nucleus (SCN), non-SCN brain and peripheral clocks, as well as cell-autonomous oscillators within virtually every cell type. A functional clock machinery on the molecular level, alignment among body clocks, as well as synchronization between endogenous circadian and exogenous environmental cycles has been shown to be crucial for our health and well-being. Yet, modern life constantly poses widespread challenges to our internal clocks, for example artificial lighting, shift work and trans-meridian travel, potentially leading to circadian disruption or misalignment and the emergence of associated diseases. For instance many of us experience a mismatch between sleep timing on work and free days (social jetlag) in our everyday lives without being aware of health consequences that may arise from such chronic circadian misalignment, Hence, this review provides an overview of the organization and molecular built-up of the mammalian circadian system, its interactions with the outside world, as well as pathologies arising from circadian disruption and misalignment.

Disrupted circadian rhythms and mental health

During the evolution of life, the temporal rhythm of our rotating planet was internalized in the form of circadian rhythms. Circadian rhythms are ~24h internal manifestations that drive daily patterns of physiology and behavior. These rhythms are entrained (synchronized) to the external environment, primarily by the light-dark cycle, and precisely controlled via molecular clocks located within the suprachiasmatic nucleus of the hypothalamus. Misalignment and/or disruption of circadian rhythms can have detrimental consequences for human health. Indeed, studies suggest strong associations between mental health and circadian rhythms. However, direct interactions between mood regulation and the circadian system are just beginning to be uncovered and appreciated. This chapter examines the relationship between disruption of circadian rhythms and mental health. The primary focus will be outlining the association between circadian disruption, in the form of night shift work, exposure to light at night, jet lag, and social jet lag, and psychiatric illness (i.e., anxiety, major depressive disorder, bipolar disorder, and schizophrenia). Additionally, we review animal models of disrupted circadian rhythms, which provide further evidence in support of a strong association between circadian disruption and affective responses. Finally, we discuss future directions for the field and suggest areas of study that require further investigation.

Health-related quality of life in pilots of a Chinese commercial airline

Health-related quality of life (HRQOL) is currently an important issue in the medical industry. However, data on HRQOL in commercial airline pilots are lacking. This study aimed to investigate HRQOL and its related factors in a sample of commercial pilots. A purposive sample of 373 participants was recruited from a Chinese Commercial Airline. The median (IQR) score for physical health, psychological health and social relationship were 64.3 (75-53.6), 62.5 (70.8-54.2) and 75 (75-58.3), respectively. The mean (SD) score for Environment was 62.2 (16). After controlling for demographics, the multiple linear regression analyses showed that physical activity, fruit intake and vegetable intake were positively correlated with HRQOL score (p < .05), while time-zone flights, smoking, alcohol drinking and being dyslipidemic showed a negative correlation with HRQOL score (p < .05). Healthcare providers should consider time-zone flights, behavioral factors and dyslipidemia when planning related health promotion and disease prevention programs for commercial pilots in the future.

The effect of jet lag on the human brain: A neuroimaging study

Jet lag is commonly experienced when travelers cross multiple time zones, leaving the wake-sleep cycle and intrinsic biological "clocks" out of synchrony with the current environment. The effect of jet lag on intrinsic cortical function remains unclear. Twenty-two healthy individuals experiencing west-to-east jet lag flight were recruited. Brain structural and functional magnetic resonance studies, as well as psychological and neurohormonal tests, were carried out when participants returned from travel over six time zones and 50 days later when their jet lag symptoms had resolved. During jet lag, the functional brain network exhibited a small-world topology that was shifted toward regularity. Alterations during jet lag relative to recovery included decreased basal ganglia-thalamocortical network connections and increased functional connectivity between the medial temporal lobe subsystem and medial visual cortex. The lower melatonin and higher thyroid hormone levels during jet lag showed the same trend as brain activity in the right lingual gyrus. Although there was no significant difference between cortisol measurements during and after jet lag, cortisol levels were associated with temporal lobe activity in the jet lag condition. Brain and neuroendocrine changes during jet lag were related to jet lag symptoms. Further prospective studies are needed to explore the time course over which jet lag acts on the human brain.