Psychomotor Vigilance Task Research Articles

Associating EEG functional networks and the effect of sleep deprivation as measured using psychomotor vigilance tests.

People are routinely forced to undertake cognitive challenges under the effect of sleep deprivation, due to professional and social obligations forcing them to ignore their circadian clock. However, low intra-individual and high inter-individual differences in behavioural outcomes are known to occur when people are sleep deprived, leading to the conclusion that trait-like differences to sleep deprivation could explain the differing levels of resilience. Within this study we consider if trait-like resilience to sleep deprivation, measured using psychomotor vigilance tests over a 40h protocol, could be associated with graph metrics (mean node strength, clustering coefficient, characteristic path length and stability) calculated from EEG functional networks acquired when participants ([Formula: see text]) are well rested (baseline). Furthermore, we investigated how stability (the consistency of a participant's functional network over time measured using 2-D correlation) changed over the constant routine. We showed evidence of strong significant correlations between high mean node strength, low characteristic path length and high stability at baseline with a general resilience to extended sleep deprivation, although the same features lead to vulnerability during the period of natural sleep onset, highlighting non-uniform correlations over time. We also show significant differences in the levels of stability between resilient and vulnerable groups.

The impact of a 20-h rotating watch schedule on cognitive and mood states in submarine operations.

This is the first study to provide valuable insights into the effects of the Israeli Navy's 20-h rotating watch schedule on submariners' alertness, mood states, risk-taking behaviours, and sleep. Specifically, we assessed the impact of the non-circadian-aligned schedule on cognitive performance, mood, and behavioural outcomes in a highly controlled submarine environment. A total of 20 male submariners participated in an at-sea mission, where their cognitive performance, mood states, risk-taking propensity, and caffeine consumption were measured. A psychomotor vigilance task (PVT) assessed alertness, the propensity for risky behaviour (Evaluation of Risks Scale) measured risk-taking behaviours, and the Profile of Mood States evaluated mood disturbances. Actigraphy was used to monitor sleep times. Data were analysed according to seven watch schedule segments. Submariners slept a mean (standard error of the mean [SEM]) of 8.3 (0.2) h/24 h, fragmented into 3.7 (0.8) h epochs. Caffeine consumption decreased at sea (mean [SEM] 149.3 [6.0] mg) compared to land (mean [SEM] 205.5 [7.2] mg; p = 0.027). In the PVT, premature responses significantly increased during Watch VI (5:00-8:00 p.m.) and Watch VII (8:00 p.m.-12:00 a.m.; p = 0.014). In the mood subscales, tension was significantly higher during Watch II (4:00-8:00 a.m.; p = 0.002), indicating greater stress. Risk-taking propensity significantly increased during afternoon shifts (p = 0.050). The 20-h watch schedule led to fragmented sleep, reduced alertness in the evening, worsened mood states in the early morning, and increased risk-taking propensity in the afternoon. These findings suggest the need for the Israeli Navy to establish evidence-based caffeine guidelines and optimise the watch schedule to improve submariners' sleep, performance, and overall well-being.

Comparison of 45-min nap versus no-nap during simulated night shift work on endothelial function: a randomized crossover feasibility trial.

Night shift workers face increased risk of cardiovascular disease (CVD) compared to non-shift workers. Evidence supports on-shift napping and regular non-invasive monitoring of endothelial function for risk mitigation, yet neither strategy is widely used. We evaluated the feasibility of non-invasive assessment of peripheral arterial tone (PAT) to assess the effect of napping during simulated night shift work on endothelial function. We used a single-site, randomized crossover trial of simulated night shift work with a 45-min nap condition versus a control, no-nap condition (ClinicalTrials.gov NCT05436951). Theprimary outcome was the number of participants with ≥ 70% of endothelial function assessments. Secondary outcomes included mean reactive hyperemia index (RHI), BP, and cognitive performance with the brief psychomotor vigilance task (PVT-B). Of the 10 consented, 9 completed both conditions. All participants exceeded feasibility benchmarks. Mean RHI did not differ by nap condition, and the delta from pre- to post measure did not differ (difference in delta = - 0.26, 95% CI - 1.09, 0.58). Hourly PVT-B assessments from 19:00 to 07:00h did not differ by nap condition. Compared to pre-nap measures, cognitive performance on the PVT-B was poorest at + 0min post-nap. Our findings can inform larger studies evaluating the effects of night shift work and napping on endothelial function. ClinicalTrials.gov (NCT05436951, registered on June 23, 2022).

Interhemispheric asynchrony of NREM EEG at the beginning and end of sleep describes evening vigilance performance in patients undergoing diagnostic polysomnography

Objective.Obstructive sleep apnea (OSA) is associated with deficits in vigilance. This work explored the temporal patterns of OSA-related events during sleep and vigilance levels measured by the psychomotor vigilance test (PVT) in patients undergoing polysomnography (PSG) for suspected OSA.Approach.The PVT was conducted prior to in-laboratory PSG for 80 patients suspected of having OSA. Three groups were formed based on PVT-RT-outcomes and participants were randomly allocated into Training (n= 55) and Test (n= 25) samples. Sleep epochs of non-rapid-eye movement (NREM) electroencephalographic (EEG) asynchrony data, and REM and NREM data for respiratory, arousal, limb movement and desaturation events were analysed. The data were segmented by sleep stage, by sleep blocks (SB) of stable Stage N2, Stage N3, mixed-stage NREM sleep (NXL), and, by Time of Night (TN) across sleep. Models associating this data with PVT groups were developed and tested.Main Results.Amodel using NREM EEG asynchrony data segmented by SB and TN achieved 81.9% accuracy in the Test Cohort. Models based on interhemispheric asynchrony SB data and OSA data segmented by TN achieved 80.6% and 79.5% respectively.Significance.Novel data segmentation methods via blocks of NXL and TN have improved our understanding of the relationship between sleep, OSA and vigilance.

Individualized rTMS Intervention Targeting Sleep Deprivation-Induced Vigilance Decline: Task fMRI-Guided Approach.

Sleep deprivation (SD) is prevalent in our increasingly round-the-clock society. Optimal countermeasures such as ample recovery sleep are often unfeasible, and brief naps, while helpful, do not fully restore cognitive performance following SD. Thus, we propose that targeted interventions, such as repetitive transcranial magnetic stimulation (rTMS), may enhance cognitive performance recovery post-SD. We recruited 50 participants for two SD experiments. In the first experiment, participants performed a psychomotor vigilance task (PVT) under three conditions: normal sleep (resting wakefulness), after 24 h of SD, and following a subsequent 30-min nap. We analyzed dynamic changes in PVT outcomes and cerebral responses across conditions to identify the optimal stimulation target. Experiment 2 adopted the same protocol except that, after the nap, 10-Hz, sham-controlled, individualized rTMS was administrated. Then, an analysis of variance was conducted to investigate the ability of stimulation to improve the PVT reaction times. Through task-related functional magnetic resonance imaging, we identified cerebral responses within the right middle frontal gyrus (MFG) as the optimal stimulation target. Subsequent application of individualized 10-Hz rTMS over the right MFG attenuated SD-induced deterioration of vigilance. Our findings suggest that combining a brief nap with individualized rTMS can significantly aid the recovery of vigilance following SD. This approach, through modulating neural activity within functional brain networks, is a promising strategy to counteract the cognitive effects of SD.

Sleep Disruption Impairs Sustained Attention in Food-Restricted Rats Using a Food-Reinforced Rodent Psychomotor Vigilance Test.

Sleep disruption (SD) impairs sustained attention, and impairment is quantified with the psychomotor vigilance test (PVT) in humans. In rats, food restriction attenuates SD's effects on sustained attention, limiting translation of rodent vigilance tests. The goal of the current study was to determine if a rodent PVT (rPVT) requiring high baseline performance using food restriction and reinforcement is sensitive to the effects of SD. Male Long-Evans rats (n=4) were trained on the rPVT using food reinforcement. Once baseline acquisition criteria were achieved, rats experienced acute SD using an automated sweep bar that moved across the home cage. Rats were tested in the rPVT the day following SD to assess performance-impairing effects. SD significantly increased lapses, and this effect was specific to shorter response-stimulus intervals. Decreased percent correct responses and increased slow reaction times were also found. These data suggest that many of the performance-impairing effects of SD are not attenuated by food restriction in this procedure. The rPVT is sensitive to the performance impairing effects of SD in food restricted rats, a common methodology used to train and maintain performance on operant behavioral tests. Thus, food restriction does not appear to attenuate the effects of SD in all attention-related behavioral procedures.

Effects of one night of sleep deprivation on whole brain intrinsic connectivity distribution using a graph theory neuroimaging approach

Neuroimaging studies have revealed disturbances in brain functional connectivity (FC) after one night of sleep deprivation (SD). These researches explored the alterations of FC using classical regions of interest (ROI)-based analysis or functional connectivity density. However, these methods need for a priori information about the selected ROIs and a specific correlation threshold to define a connection between two ROIs or voxels, which may bring inconsistent results. In the present study, we adopted a data-driven, whole brain voxel-based graph-theoretical approach, intrinsic connectivity distribution (ICD) analysis, to examine changes of brain connectivity after SD in 52 normal young subjects without any prior knowledge. The cross-hemisphere ICD (ch-ICD) analysis was also performed to discover the effect of SD on cerebral lateralization. We found that sleep-deprived subjects showed significant reduced ICD in default mode network (DMN) and limbic network, and increased ICD in sensorimotor network. Furthermore, after SD, the ICD in the right precuneus showed significant correlation with psychomotor vigilance test (PVT) performance following the stepwise regression analysis after Bonferroni correction (ICD = 0.43 - 0.62*10% fast reaction time + 0.31*the standard deviation of reaction time, p = 0.0012). Follow-up seed-based FC analyses in the right precuneus revealed decreased FC to regions in DMN, visual network, ventral attentional network and frontal-parietal network. Nevertheless, no striking difference of ch-ICD was found following SD. In conclusion, these findings suggested that DMN, especially precuneus may be hubs of FC disturbances associated with vigilance after SD, and may provide new insights into the intervention for SD.

Decoding the influence of emotional and attentional states on self-control using facial analysis

Self-control plays a pivotal role in pursuing long-term goals related to health and financial well-being. While ample evidence suggests that humans are prone to occasional self-control lapses, little is known about how changes in emotional and attentional states affect the ability to maintain self-control. In two studies (N1 = 109 and N2 = 90), we used emotion recognition software to decode participants’ facial expressions while manipulating their attentional and emotional states during a Psychomotor Vigilance Task (PVT) before exerting self-control in a subsequent task. Our findings reveal dissociable roles of attention and valence in maintaining self-control, depending on the distinct demands of the task. Specifically, performance in a subsequent cognitive task was predominantly associated with changes in attentional states during the PVT rather than valence. Conversely, preferences in a subsequent social task were associated with changes in valence states during the PVT, while attention showed no effect. This dissociation between attention-invoked and emotion-invoked lapses in self-control holds significant implications for psychological and economic models of self-control, ultimately contributing to the development of policies to mitigate the detrimental consequences of individual self-control lapses.

Modeling Sensor-based Vigilance Decrement in the Healthcare Environment

Vigilance refers to an individual’s ability to maintain attention over time. Vigilance decrement is particularly concerning in clinical environments where shift work and long working hours are common. This study identifies significant factors and indicators for predicting and monitoring individuals’ vigilance decrement. We enrolled 11 participants and measured their vigilance levels by recording their reaction times while completing the Psychomotor Vigilance Test. Additionally, we measured participants’ physiological responses and collected their sleep deprivation data, demographic information, and self-reported anxiety levels. Using repeated-measures correlation analysis, we found that decreased vigilance levels, indicated by longer reaction times, were associated with higher electrodermal activity ( p < .01), lower skin temperature ( p < .001), shorter fixation durations ( p < .05), and increased saccade frequency ( p < .05). Moreover, sleep deprivation significantly affected vigilance decrement ( p < .001). Our findings provide the potential to develop a predictive model of vigilance decrements using physiological signals collected from non-intrusive devices, as an alternative to current behavior-based methods.

InfoFlowNet: A multi-head attention-based self-supervised learning model with surrogate approach for uncovering brain effective connectivity

Deciphering brain network topology can enhance the depth of neuroscientific knowledge and facilitate the development of neural engineering methods. Effective connectivity, which gauges the directional influences among brain regions, is pivotal for these studies. This research introduces InfoFlowNet, a novel self-supervised learning model designed to infer causal relationships in electroencephalogram (EEG) data, aiming at capturing the complex information flow among brain regions. Specifically, InfoFlowNet employs convolution operations and multi-head self-attention mechanisms with a masking feature, which ignores self-connections to focus on inter-regional dynamics. Additionally, a new causal magnitude estimation is introduced by assessing the impact of shuffled surrogate data on signal prediction to quantify causal influence. Experiments using synthetic data and real EEG datasets demonstrate that InfoFlowNet effectively uncovers time-varying causal relationships. Compared with the Granger causality model (GCM) and the temporal causal discovery framework (TCDF), InfoFlowNet shows superior sensitivity in detecting significant causal edges. For instance, in a psychomotor vigilance task, InfoFlowNet identified 8 out of 16 significant causal edges, significantly outperforming GCM and TCDF. Furthermore, InfoFlowNet successfully passes the whiteness test on the model's residuals, and advanced analyses illustrate the advantages of utilizing multi-head attention and masking mechanisms to capture effective connectivity. In sum, InfoFlowNet represents a significant advancement in the analysis of effective connectivity, offering a deeper understanding of brain network dynamics. The model's ability to discern complex causal interactions supports its potential application in broader neuroscientific research and applications.

Sleep restriction and age effects on distinct aspects of cognition in adolescents.

Insufficient sleep negatively impacts scholastic performance in children and adolescents. Here we use a dose response time in bed (TIB) restriction study to evaluate associations between sleep loss and multiple aspects of cognition. We evaluated changes in cognitive measures across ages 10 to 23 years and determined whether the effects of sleep loss changed across this age range. A younger cohort (n=77, age range 9.9 to 16.2 years) was studied annually for 3 years. An older cohort study (n=82, age range 15 to 22.8 years) was interrupted by the COVID pandemic with 25 participants completing multiple years. Annually participants completed each of three TIB conditions: four consecutive nights with 7, 8.5, or 10h in bed. A day of cognitive testing followed the fourth night. Restricting TIB to 7h was associated with impaired top-down attentional control and cognitive flexibility, but performance did not differ between the 8.5 and 10h TIB conditions. Psychomotor vigilance test performance decreased as TIB was restricted from 10 to 8.5h and decreased further with restriction to 7h. Sternberg test measures of working memory were not significantly affected by TIB restriction. The effects of sleep loss on these cognitive measures did not change significantly with age, but age-related improvement in many of the measures may compensate for some sleep loss effects. The findings here do not indicate an adolescent decrease in sleep need; however, the minimal duration of sleep needed for optimal performance appears to differ depending on the cognitive measure.

Effects of job demands, job resources, personal resources on night-shift alertness of ICU shift nurses: a cross‑sectional survey study based on the job demands-resources model

BackgroundA positive work environment can enhance nursing safety and patient satisfaction while alleviating nurse stress. Conversely, a poor work environment can harm nurses’ physical and mental health and compromise the quality of care, particularly in the high-intensity and shift-based setting of the ICU.ObjectivesBased on the Job demands-resources (JD-R) model, this study examined the effects of job demands and job resources in the work environment, as well as personal resources, on the night-shift alertness of ICU shift nurses.MethodsThis cross-sectional correlational exploratory study, conducted from July to September 2022, recruited 291 ICU shift nurses from a hospital in Beijing, China. The Copenhagen Psychosocial Questionnaire (COPSOQ), the Self-resilience scale, the General Self-Efficacy Scale (GSES), and the Psychomotor Vigilance Task (PVT) were used to subjectively and objectively measure the job demands, job resources, personal resources, and night-shift alertness. SPSS 26.0 and Mplus 8.3 were used to analyze the data and construct the structural equation model.ResultsThe night-shift reaction time was 251.0 ms (Median), indicating a relatively high level of alertness. Job demands were negatively correlated with both job resources (r=-0.570, P < 0.001) and personal resources (r=-0.462, P < 0.001), while a positive correlation existed between job resources and personal resources (r = 0.554, P < 0.001). The results show that increased job demands can lead to higher levels of nurse strain (β = 0.955, P < 0.001), whereas job resources were found that it can decrease strain (β=-0.477, P = 0.047). Adequate job resources can enhance motivation directly (β = 0.874, P < 0.001), subsequently reducing reaction time (β=-0.148, P = 0.044) and improving night-shift alertness among ICU shift nurses.ConclusionEnhancing ICU shift nurses’ work motivation through bolstering job resources can boost night-shift alertness. However, it is noteworthy that, in this study, neither strain nor individual resources significantly influenced nurses’ night-shift alertness. This may be attributed to the complexity of the ICU environment and individual differences. Future research should explore the relationship between these factors and nurses’ work alertness.

An Evaluation of the Autonomic Nervous Activity and Psychomotor Vigilance Level for Smells in the Work Booth

In this study, we investigated the effects of the smell environment in the work booth on autonomic nervous activity (ANS) and psychomotor vigilance levels (PVLs) using linalool (LNL) and trans-2-nonenal (T2N). The subjects were six healthy males (31 ± 6 years old) and six healthy females (24 ± 5 years old). They sat in the work booth filled with the smells of LNL and T2N for 10 min, and their electrocardiograms (ECGs), skin conductance levels, pulse wave variabilities, skin temperatures, and seat pressure distributions were measured. In addition, the orthostatic load test (OLT) and psychomotor vigilance test (PVT) were performed before and after entering the work booth, and a subjective evaluation of the smell was also performed after the experiment. This paper focused on ECG and PVT data and analyzed changes in heart rate variability indices and PVT scores. Males felt slightly comfortable with the LNL smell and showed promoted sympathetic nerve activity in the OLT after the smell presentation. Females felt slightly uncomfortable with the T2N smell and showed promoted sympathetic nerve activity and a decrease in PVT scores in the OLT after the smell presentation. Gender differences were observed in ANS and PVLs, and it is possible that the comfort of LNL increased sympathetic nervous activity in males, while the uncomfortableness of T2N may have reduced work performance in females.

Locus coeruleus microstructural integrity is associated with vigilance vulnerability to sleep deprivation.

Insufficient sleep compromises cognitive performance, diminishes vigilance, and disrupts daily functioning in hundreds of millions of people worldwide. Despite extensive research revealing significant variability in vigilance vulnerability to sleep deprivation, the underlying mechanisms of these individual differences remain elusive. Locus coeruleus (LC) plays a crucial role in the regulation of sleep-wake cycles and has emerged as a potential marker for vigilance vulnerability to sleep deprivation. In this study, we investigate whether LC microstructural integrity, assessed by fractional anisotropy (FA) through diffusion tensor imaging (DTI) at baseline before sleep deprivation, can predict impaired psychomotor vigilance test (PVT) performance during sleep deprivation in a cohort of 60 healthy individuals subjected to a rigorously controlled in-laboratory sleep study. The findings indicate that individuals with high LC FA experience less vigilance impairment from sleep deprivation compared with those with low LC FA. LC FA accounts for 10.8% of the variance in sleep-deprived PVT lapses. Importantly, the relationship between LC FA and impaired PVT performance during sleep deprivation is anatomically specific, suggesting that LC microstructural integrity may serve as a biomarker for vigilance vulnerability to sleep loss.

The Effect of Meal Frequency and Glycemic Index During the Night Shift on Alertness, Hunger, and Gastrointestinal Complaints in Female Health Care Workers—A Two-Armed Randomized Crossover Trial

BackgroundNutrition strategies for night-shift workers could optimize alertness and minimize hunger and reduce gastrointestinal complaints, enhancing safety and well-being. ObjectivesThis study aimed to investigate the effects of 1 or 3 small meals, with either low or high glycemic index (GI), compared with no meal, on alertness, hunger, and gastrointestinal complaints during the night shift. MethodsFifty-one female health care workers, aged 18 to 61 Y, participated in a 2-armed randomized crossover design. In 1 study arm, participants received 1 yogurt meal during the night shift, AND in the other, they received 3. Each study arm involved 3 intervention periods during night shifts, with participants consuming yogurt with low GI (1LGI or 3LGI) OR high GI (1HGI or 3HGI) carbohydrates, or no meal (0NGI). Objective alertness was assessed using a validated brief psychomotor vigilance task (PVT-B), subjective alertness with the Samn–Perelli scale, and hunger and gastrointestinal complaints through questionnaires. ResultsParticipants in the 1LGI (β: −4.6; 95% CI: 0.0, 9.3) and 3LGI (β: −3.4; 95% CI: 0.0, 6.8) conditions had fewer lapses during the PVT-B than those in the 3HGI condition. No differences were found between meal conditions for median and reciprocal reaction time or subjective alertness. All 4 conditions reported less hunger (β: from −0.6 to −1.2) compared with no meal. The 3LGI condition resulted in more rumbling intestines than the 3HGI (β: 1.1; 95% CI: 0.4, 1.7) and 0NGI (β: 0.74; 95% CI: 0.11, 1.37) conditions. ConclusionsOur study suggests that consuming 3 small low GI meals during the night shift helps maintain alertness and reduces lapses compared with 3 high GI meals. It also minimizes hunger but may cause mild gastrointestinal complaints.This trial was registered at International Clinical Trial Registry (https://trialsearch.who.int/Trial2.aspx?TrialID%3dNL-OMON25574).

Acute Aerobic Exercise Intensity on Working Memory and Vigilance After Nap Deprivation: Effects of Low-Intensity Deserve Attention.

Napping deprivation in habitual nappers leads to cognitive impairment. The ameliorative effect of acute aerobic exercise has been demonstrated for this post-cognitive impairment. However, it is still unclear which intensity of aerobic exercise is the most effective and how long this improvement can be sustained. Fifty-eight healthy adults with a chronic napping habit were randomly assigned to four intervention groups after undergoing nap deprivation: a sedentary control group, a low-intensity exercise group (50-59% maximum heart rate, HRmax), a moderate-intensity exercise group (60-69% HRmax), and a high-intensity exercise group (70-79% HRmax). Working memory (N-back task), vigilance (Psychomotor Vigilance Task, PVT), and response inhibitory capacity (Go/NoGo task) were measured. Regression analyses showed a quadratic trend between exercise intensity and working memory reaction time and accuracy (F =3.297-5.769, p < 0.05, R2 =10.7-18.9%). The effects of exercise were optimal at low-intensity. There was a significant quadratic trend between exercise intensity and PVT lapse (F =4.314, p =0.042, R² =7.2%). The effect of exercise increased with higher intensity. Prolonged observation found that the effect of low-intensity exercise on working memory was maintained for 2 hours. The effect of low-intensity exercise might be underestimated. Low-intensity exercise significantly improved working memory performance, and the effects could be maintained throughout the afternoon. In contrast, the effects of high-intensity exercise were unlikely to be maintained and might even have negative effects. Future researchers can broaden the categories of participants to enhance the external validity and collect diverse physiological indicators to explore related physiological mechanisms.

Cognitive performance during exposure to moderate normobaric hypoxia after sleep restriction: Relationship to physiological and stress biomarkers

IntroductionExposure to moderate levels of simulated hypoxia has subtle cognitive effects relative to ground level, in healthy individuals. However, there are few data on the cognitive consequences of the combination of hypoxia and partial sleep deprivation, which is a classic military or civilian operational context. In this study, we tested the hypothesis that exposure to moderate hypoxia while sleep-restricted impairs several domains of cognition, and we also assessed physiological parameters and salivary concentrations of cortisol and alpha-amylase. MethodSeventeen healthy males completed two sessions of cognitive tests (sustained attention using the PVT psychomotor vigilance task and executive functions using the Go-NoGo inhibition task and N-Back working memory task) after 30 min (T + 30′) and 4 h (T + 240′) of exposure in a normobaric hypoxic tent (FIO2 = 13.6 %, ≃ 3,500 m) (HY). This was completed after one night of sleep restriction (3 a.m. to 6 a.m. bedtime, SRHY) and one night of habitual sleep (10 p.m. to 6 a.m. bedtime, HSHY) (with cross-over randomization). The two nights sleep architecture and physiological parameters (oxygen saturation (SpO2) and heart rate (HR) during T + 30′ and T + 240′sessions were analyzed. Salivary cortisol and alpha-amylase (sAA) concentrations were analyzed before hypoxia, after the T + 30′ and T + 240′ cognitive sessions, and after leaving the hypoxic tent. ResultsSustained attention (RT and number of lapses in the PVT) and executive functions (Go-NoGo and 1-Back and 2-Back parameters, as inhibition and working memory signatures) were impaired in the SRHY condition compared to HSHY. SpO2 and HR were higher after 4 h compared with 30 min of hypoxia in the HSHY condition, while only HR was statistically higher in the SRHY condition. In SRHY, salivary AA concentration was lower and cortisol was higher than in HSHY. A significant increase in sAA concentration is observed after the cognitive session at 4 h of hypoxia exposure compared to that at 30 min, only in the SRHY condition. There are significant positive correlations between reaction time and the corresponding heart rate (a non-invasive marker of physiological stress) for the executive tasks in the two sleep conditions. This was not observed for salivary levels of sAA and cortisol, respective reliable indicators of the sympathoadrenomedullary system and the hypothalamic-pituitary adrenocortical system. ConclusionExposure to moderate normobaric hypoxia (≃ 3500 m / ≃ 11,500 ft simulated) after a single night of 3-hour sleep impairs cognitive performance after 30 min and 4 h of exposure. The key determinants and/or mechanism(s) responsible for cognitive impairment when exposed to moderate hypoxia with sleep restriction, particularly on the executive function, have yet to be elucidated.

Tracking Vigilance Fluctuations in Real-Time: A Sliding-Window HRV-based Machine-Learning Approach.

Heart rate variability (HRV)-based machine learning models hold promise for real-world vigilance evaluation, yet their real-time applicability is limited by lengthy feature extraction times and reliance on subjective benchmarks. This study aimed to improve the objectivity and efficiency of HRV-based vigilance evaluation by associating HRV and behavior metrics through a sliding-window approach. Forty-four healthy adults underwent psychomotor vigilance tasks under both well-rested and sleep-deprived conditions, with simultaneous electrocardiogram recording. A sliding-window approach (30s length, 10s step) was used for HRV feature extraction and behavior assessment. Repeated-measures ANOVA was used to examine how HRV related to objective vigilance levels. Stability selection technique was applied for feature selection, and the vigilance ground truth-high (fastest 40%), intermediate (middle 20%), and low (slowest 40%)-were determined based on each participant's range of performance. Four machine-learning classifiers-k-nearest neighbours, support vector machine (SVM), AdaBoost, and random forest-were trained and tested using cross-validation. Fluctuated vigilance performance indicated pronounced state instability, particularly after sleep deprivation. Temporary decrements in performance were associated with a decrease in heart rate and an increase in time-domain heart rate variability. SVM achieved the best performance, with a cross-validated accuracy of 89% for binary classification of high versus low vigilance epochs. Overall accuracy dropped to 72% for three-class classification in leave-one-participant-out cross-validation, but SVM maintained a precision of 84% in identifying low-vigilance epochs. Sliding-window-based HRV metrics would effectively capture the fluctuations in vigilance during task execution, enabling more timely and accurate detection of performance decrement.

Effects of isolated and combined mental and physical fatigue on motor skill and endurance exercise performance

BackgroundMental fatigue, elicited by cognitive demands, can impair sport and exercise performance. The effects of isolated mental fatigue on performance are well documented but few studies have explored the effects of combined mental and physical fatigue on skilled motor and endurance exercise performance. ObjectiveThis study explored the effects of isolated mental, isolated physical, and combined (mental plus physical) fatigue on skill and exercise task performance. Method164 athletes were randomly assigned to 1 of 4 groups: mental fatigue, physical fatigue, combined fatigue, control (no fatigue). Mental fatigue was induced by a 15-min time-load dual-back cognitive task. Physical fatigue was induced by a 90-s burpee exercise task. Next, all participants completed a throwing skill task and performed burpee exercises to failure. Objective (brief Psychomotor Vigilance Task, PVT-B) and subjective (self-report) measures of mental fatigue and Ratings of Perceived Exertion were obtained throughout. ResultsThe mental fatigue and combined fatigue groups performed the worst on both the throwing and burpee tasks compared with the physical fatigue and control groups. The former reported higher mental fatigue throughout and had worse response accuracy and variation on the end-of-session PVT-B task. The combined fatigue group performed better than the mental fatigue group on the throwing and burpee tasks. ConclusionA demanding cognitive task induced a state of mental fatigue and impaired skill and endurance performance. Mental fatigue alone was more detrimental than combined fatigue to skill and endurance performance, suggesting that the physical activity manipulation reduced the negative effects of mental fatigue on performance.

Impact of carbon dioxide exposures on sleep latency among healthy volunteers: A randomized order, paired crossover study, evidence from the multiple sleep latency test

BackgroundDaytime sleepiness affects work efficiency, occupational safety, and public health. Although previous studies have reported an association between environmental carbon dioxide (eCO2) and daytime sleepiness, it has been challenging to draw a firm conclusion due to the lack of standardized sampling and profiling protocols. ObjectiveWe examined the effect of pure CO2 exposure at 5000 (ppm, parts per million) on daytime sleepiness. MethodsEleven healthy participants (males of 24 ± 3 years, mean ± SD) completed a four-nap multiple sleep latency test (MSLT) protocol in the environmentally controlled chamber under two conditions: the CO2 condition (4851 ± 229 ppm) and the Control condition (1102 ± 204 ppm). The subjective sleepiness level and cognitive performances were also evaluated using the Stanford Sleepiness Scale (SSS) questionnaire, Psychomotor Vigilance Test (PVT), and Stroop test after each nap session. ResultsA significant reduction in sleep latency was observed in the CO2 exposure condition (Control vs. CO2 = 13.1 ± 3.3 min vs. 9.7 ± 3.2 min). The subjective sleepiness scores were also significantly higher in the CO2 exposure condition than in the Control condition (Control vs. CO2 = 2.7 ± 0.5 vs. 4.7 ± 0.8). Cognitive responses after naps showed no significant difference across conditions. ConclusionThis study revealed that exposure to environmental CO2 at a concentration as high as the upper safety limit at work sites significantly shortened the sleep latency and enhanced subjective sleepiness during naps in the MSLT without affecting cognitive responses after each exposure. Our results demonstrated that exposure to high environmental CO2 induces daytime sleepiness that potentially compromises work efficiency and safety.