Measuring sleep parameters of naval sailors: A comparison between subjective self-report and wrist actigraphy.

Wrist actigraph and self-report activity logs were used in a Royal Canadian Navy's at-sea exercise to track sleep patterns of naval personnel. In this study, we compared sleep parameters obtained from two measurement methods and investigated their intrinsic biases. The results revealed a strong agreement between two methods for recording sleep offset times, but a relatively poor agreement for parameters that include substantial periods of transition between sleep and wake states. Overall, self-reported sleep durations were substantially longer than actigraphic estimates (mean bias of -30.6 min; limits of agreement -95.9 to 34.8 min), and the discrepancy was mainly caused by differences in two methods to track sleep onset latency and Wake-up After Sleep Onset (WASO). Based on a customised activity log, a strong positive correlation (rho = 0.75, p < .001) between self-report and actigraphy was observed for sleep duration estimates, which confirmed the effectiveness of the activity log in field studies. Between two participant groups with different work schedules, the agreement between self-report and actigraphy was consistently better for day workers than watch keepers. The findings inform future sleep research planning that involves naval personnel in field settings.

Reliability of venous gas embolism detection in the subclavian area for decompression stress assessment following scuba diving.

INTRODUCTION: Ultrasonic detection of venous gas emboli (VGE) in the precordial (PRE) region is commonly used in evaluation of decompression stress. While subclavian (SC) VGE detection can also be used to augment and improve the evaluation, no study has rigorously compared VGE grades from both sites as decompression stress indicators. METHODS: This retrospective study examined 1,016 man-dives breathing air extracted from the Defence Research and Development Canada dataset. Data for each man-dive included dive parameters (depth, bottom time, total ascent time), PRE and SC VGE grades (Kisman-Masurel) and post-dive decompression sickness (DCS) status. Correlation between SC and PRE grades was analyzed and the association of the probability of DCS (pDCS) with dive parameters and high bubble grades (HBG III- to IV) was modelled by logistic regression for SC and PRE separately for DCS risk ratio comparisons. RESULTS: PRE and SC VGE grades were substantially correlated (R = 0.66) and were not statistically different (p = 0.61). For both sites, pDCS increased with increasing VGE grade. When adjusted for dive parameters, the DCS risk was significantly associated with HBG for both PRE (p = 0.03) and SC (p < 0.001) but the DCS risk ratio for SC HBG (RR = 6.0, 95% CI [2.7-12.3]) was significantly higher than for PRE HBG (RR = 2.6, 95% CI [1.1-6.0]). CONCLUSIONS: The association of bubble grades with DCS occurrence is stronger for SC than PRE when exposure severity is taken into account. The usefulness of SC VGE in decompression stress evaluation has been underestimated in the past.

Acute Mild Hypoxic Hypoxia Effects on Cognitive and Simulated Aircraft Pilot Performance.

BACKGROUND: The effects of acute mild hypoxic hypoxia (HH) and physical activity on physiological measures, signs and symptoms, mood, fatigue, cognition, and performance on a simulated flight task were investigated between 8000 (8K; 2438 m) and 14,000 ft (14K; 4267 m). METHOD: In a hypobaric chamber, 16 military helicopter pilots were randomly exposed to 4 altitudes and 3 physical exertion levels. After each exercise period, participants identified targets on a designated flight path on a desktop simulator and completed a cognitive test battery. Cerebral regional and finger pulse oxyhemoglobin saturation levels (rSO2 and Spo2), heart and respiration rates were continuously monitored. Participants indicated their symptoms, mood and fatigue. RESULTS: rSO2 and Spo2 were affected by the increase of altitude and exercise level. Target identification accuracy and latency within the simulated flight task showed decrements at 8K, 10K (3048 m), 12K (3658 m), and 14K. Cognitive performance was degraded at 14K. More than 60% of the participants at 8K and 10K and more than 80% at 12K and 14K reported symptoms. Altitude increased symptoms, negative mood, general fatigue, and physical fatigue. DISCUSSION: Our findings indicate a significant influence of mild HH on a number of outcome measures at altitudes above 10K, where operational restrictions are well established. In contrast, there was no clear influence of HH on performance at lower altitudes (i.e., 8K and 10K). The occurrence of HH symptoms and the decrements in target identification latency and accuracy at 8K and 10K may negatively impact flight performance and require further study.Bouak F, Vartanian O, Hofer K, Cheung B. Acute mild hypoxic hypoxia effects on cognitive and simulated aircraft pilot performance. Aerosp Med Hum Perform. 2018; 89(6):526-535.

An improved model to predict performance under mental fatigue.

Fatigue has become an increasing problem in our modern society. Using MATLAB as a generic modelling tool, a fatigue model was developed based on an existing one and compared with a commercial fatigue software for prediction of cognitive performance under total and partial sleep deprivation. The flexibility of our fatigue model allowed additions of new algorithms and mechanisms for non-sleep factors and countermeasures and thus improved model predictions and usability for both civilian and military applications. This was demonstrated by model simulations of various scenarios and comparison with experimental studies. Our future work will be focused on model validation and integration with other modelling tools. Practitioner Summary: Mental fatigue affects health, safety and quality of life in our modern society. In this paper, we reported a cognitive fatigue model based on existing models with newly incorporated components taking both the operator's state of alertness and task demand into account. The model provided the additional capability for prediction of cognitive performance in scenarios involving pharmaceutical countermeasures, different task demands and shift work.

Task switching following 24 h of total sleep deprivation: a functional MRI study.

Task switching is a ubiquitous feature of many human activities that involve multitasking. In addition, owing to occupational demands, many individuals are required to engage in task switching under various levels of sleep deprivation, such as those who work in military and medical contexts. Nevertheless, little is known about the effects that sleep loss has on the neural bases of task switching. To address this shortcoming, we administered a cued switching task to participants following a night of normal sleep and also following a night of total sleep deprivation - in counterbalanced order. The behavioral results demonstrated a cost (i.e. longer reaction time) both as a function of sleep deprivation and task switching. Sleep deprivation resulted in greater activation in the frontoparietal network, whereas task switching was correlated with greater activation in the thalamus and superior temporal gyrus. However, despite increases in fatigue and sleepiness and a reduction in cognitive effectiveness (computed from actigraphic data), the reaction time cost associated with switching (i.e. switch cost) was not exacerbated by sleep deprivation. The results are discussed in terms of the involvement of executive functions in mitigating the effects of sleep deprivation on task switching.

Transfer of training from one working memory task to another: behavioural and neural evidence.

N-back working memory (WM) tasks necessitate the maintenance and updating of dynamic rehearsal sets during performance. The delayed matching-to-sample (dMTS) task is another WM task, which in turn involves the encoding, maintenance, and retrieval of stimulus representations in sequential order. Because both n-back and dMTS engage WM function, we hypothesized that compared to a control task not taxing WM, training on the n-back task would be associated with better performance on dMTS by virtue of training a shared mental capacity. We tested this hypothesis by randomly assigning subjects (N = 43) to train on either the n-back (including 2-back and 3-back levels) or an active control task. Following training, dMTS was administered in the fMRI scanner. The n-back group performed marginally better than the active control group on dMTS. In addition, although the n-back group improved more on the less difficult 2-back level than the more difficult 3-back level across training sessions, it was improvement on the 3-back level that accounted for 21% of the variance in dMTS performance. For the control group, improvement in training across sessions was unrelated to dMTS performance. At the neural level, greater activation in the left inferior frontal gyrus, right posterior parietal cortex, and the cerebellum distinguished the n-back group from the control group in the maintenance phase of dMTS. Degree of improvement on the 3-back level across training sessions was correlated with activation in right lateral prefrontal and motor cortices in the maintenance phase of dMTS. Our results suggest that although n-back training is more likely to improve performance in easier blocks, it is improvement in more difficult blocks that is predictive of performance on a target task drawing on WM. In addition, the extent to which training on a task can transfer to another task is likely due to the engagement of shared cognitive capacities and underlying neural substrates-in this case WM.

The effects of a single night of sleep deprivation on fluency and prefrontal cortex function during divergent thinking.

The dorsal and ventral aspects of the prefrontal cortex (PFC) are the two regions most consistently recruited in divergent thinking tasks. Given that frontal tasks have been shown to be vulnerable to sleep loss, we explored the impact of a single night of sleep deprivation on fluency (i.e., number of generated responses) and PFC function during divergent thinking. Participants underwent functional magnetic resonance imaging scanning twice while engaged in the Alternate Uses Task (AUT) - once following a single night of sleep deprivation and once following a night of normal sleep. They also wore wrist activity monitors, which enabled us to quantify daily sleep and model cognitive effectiveness. The intervention was effective, producing greater levels of fatigue and sleepiness. Modeled cognitive effectiveness and fluency were impaired following sleep deprivation, and sleep deprivation was associated with greater activation in the left inferior frontal gyrus (IFG) during AUT. The results suggest that an intervention known to temporarily compromise frontal function can impair fluency, and that this effect is instantiated in the form of an increased hemodynamic response in the left IFG.

A physiologically based pharmacokinetics model for melatonin--effects of light and routes of administration.

Physiologically based pharmacokinetic (PBPK) models were developed using MATLAB Simulink(®) to predict diurnal variations of endogenous melatonin with light as well as pharmacokinetics of exogenous melatonin via different routes of administration. The model was structured using whole body, including pineal and saliva compartments, and parameterized based on the literature values for endogenous melatonin. It was then optimized by including various intensities of light and various dosage and formulation of melatonin. The model predictions generally have a good fit with available experimental data as evaluated by mean squared errors and ratios between model-predicted and observed values considering large variations in melatonin secretion and pharmacokinetics as reported in the literature. It also demonstrates the capability and usefulness in simulating plasma and salivary concentrations of melatonin under different light conditions and the interaction of endogenous melatonin with the pharmacokinetics of exogenous melatonin. Given the mechanistic approach and programming flexibility of MATLAB Simulink(®), the PBPK model could provide predictions of endogenous melatonin rhythms and pharmacokinetic changes in response to environmental (light) and experimental (dosage and route of administration) conditions. Furthermore, the model may be used to optimize the combined treatment using light exposure and exogenous melatonin for maximal phase advances or delays.

Right inferior frontal gyrus activation as a neural marker of successful lying.

There is evidence to suggest that successful lying necessitates cognitive effort. We tested this hypothesis by instructing participants to lie or tell the truth under conditions of high and low working memory (WM) load. The task required participants to register a response on 80 trials of identical structure within a 2 (WM Load: high, low) × 2 (Instruction: truth or lie) repeated-measures design. Participants were less accurate and responded more slowly when WM load was high, and also when they lied. High WM load activated the fronto-parietal WM network including dorsolateral prefrontal cortex (PFC), middle frontal gyrus, precuneus, and intraparietal cortex. Lying activated areas previously shown to underlie deception, including middle and superior frontal gyrus and precuneus. Critically, successful lying in the high vs. low WM load condition was associated with longer response latency, and it activated the right inferior frontal gyrus-a key brain region regulating inhibition. The same pattern of activation in the inferior frontal gyrus was absent when participants told the truth. These findings demonstrate that lying under high cognitive load places a burden on inhibition, and that the right inferior frontal gyrus may provide a neural marker for successful lying.

Negative valence can evoke a liberal response bias in syllogistic reasoning.

Recently, studies have demonstrated that negative valence reduces the magnitude of the belief-bias effect in syllogistic reasoning. This effect has been localized in the reasoning stage, in the form of increased deliberation on trials where validity and conclusion believability are incongruent. Here, using signal detection theory, we show that the attenuation of belief bias observed when valence was negative can also be evoked by a liberal response bias at the decision stage. Indeed, when valence was negative participants adopted a more liberal criterion for judging syllogisms as "valid," and were overconfident in their judgments. They also displayed less sensitivity in distinguishing between valid and invalid syllogisms. Our findings dovetail with recent evidence from memory research suggesting that negative valence can evoke a liberal response bias without improving performance. Our novel contribution is the demonstration that the attenuating effect of negative valence on belief bias can take multiples routes--by influencing the decision stage as was the case here, the reasoning stage as has been demonstrated elsewhere, and potentially both stages.

Tactile cueing in detecting and controlling pitch and roll motion.

BACKGROUND: Tactile cueing has been explored primarily for the detection of linear motion such as vertical, longitudinal, and lateral translation in the laboratory and in flight. The usefulness of tactile cues in detecting roll and pitch motion has not been fully investigated. METHODS: There were 12 subjects (21-56 yr) who were exposed to controlled pitch and roll motion generated by a motion platform with and without tactile cueing. The tactile system consists of a torso vest with 24 electromechanical tactors and a tactor on each shoulder and under each thigh harness, respectively. While devoid of visual and auditory cues, each subject performed three tasks: 1) indicate motion perception without tactile cues (C1); 2) return to vertical from an offset angle (C2); and 3) maintain straight and level while the platform was continuously in motion (C3). RESULTS: Our results indicated that in the absence of visual and auditory cues, subjects reported that the tactile system was useful in the execution of C2 and C3 maneuvers. Specifically, the presence of tactile cues had a significant impact on the accuracy, duration, and perceived workload. In addition, tactile cueing also increased the accuracy in returning to neutral from an offset position and in maintaining the neutral position while the platform was in continuous motion. CONCLUSIONS: Tactile cueing appears to be effective in detecting roll and pitch motion and has the potential to reduce the workload and risks of high stress and time sensitive air operations.