Slow release caffeine and prolonged (64-h) continuous wakefulness: effects on vigilance and cognitive performance

Concentration-effect relationships of plasma caffeine on EEG delta power and cardiac autonomic activity during human sleep

Acute caffeine intake affects brain and cardiovascular physiology, yet the concentration-effect relationships on the electroencephalogram and cardiac autonomic activity during sleep are poorly understood. To tackle this question, we simultaneously quantified the plasma caffeine concentration with ultra-high-performance liquid chromatography, as well as the electroencephalogram, heart rate and high-frequency (0.15-0.4 Hz) spectral power in heart rate variability, representing parasympathetic activity, with standard polysomnography during undisturbed human sleep. Twenty-one healthy young men in randomized, double-blind, crossover fashion, ingested 160 mg caffeine or placebo in a delayed, pulsatile-release caffeine formula at their habitual bedtime, and initiated a 4-hr sleep opportunity 4.5 hr later. The mean caffeine levels during sleep exhibited high individual variability between 0.2 and 18.4 μmol L-1 . Across the first two non-rapid-eye-movement (NREM)-rapid-eye-movement sleep cycles, electroencephalogram delta (0.75-2.5 Hz) activity and heart rate were reliably modulated by waking and sleep states. Caffeine dose-dependently reduced delta activity and heart rate, and increased high-frequency heart rate variability in NREM sleep when compared with placebo. The average reduction in heart rate equalled 3.24 ± 0.77 beats per minute. Non-linear statistical models suggest that caffeine levels above ~7.4 μmol L-1 decreased electroencephalogram delta activity, whereas concentrations above ~4.3 μmol L-1 and ~ 4.9 μmol L-1 , respectively, reduced heart rate and increased high-frequency heart rate variability. These findings provide quantitative concentration-effect relationships of caffeine, electroencephalogram delta power and cardiac autonomic activity, and suggest increased parasympathetic activity during sleep after intake of caffeine.

Comparative Bioavailability and Benefits on Mental Functions of Novel Extended-Release Caffeine Capsules against Immediate-Release Caffeine Capsules: An Open-Label, Randomized, Cross-over, Single-Dose Two-Way Crossover Study

Present study aimed compared pharmacokinetic profile of sustained-release CaffXtend® capsules (SR-Caffeine) with immediate-release caffeine capsules (IR-Caffeine), and the effect of SR-caffeine on memory, motivation, concentration, and attention. This open-label, randomized, single-dose, two-treatment, two-sequence, two-period, two-way crossover oral bioavailability study block randomized (1:1) healthy subjects (N = 15) to receive SR-Caffeine (200 mg) and IR-Caffeine (200 mg). Blood samples were collected at 0.25, 0.50, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12, 24, 36 and 48 h in each period. Primary study outcome included comparing relative bioavailability of SR-Caffeine 200 mg and IR-Caffeine 200 mg under fasting conditions, and changes in caffeine research visual analogue scale (Caff-VAS) scores ('relaxed', 'alert', 'jittery', 'tired', 'tense', 'headache', 'overall mood' and 'mentally fatigued') were also evaluated. Fifteen subjects completed the study. Mean tmax was 4.08 ± 2.13h for SR-Caffeine compared to 0.83 ± 0.39h for IR-Caffeine, (p < 0.0001). Similarly, mean t½ was 7.07 ± 3.48h for SR-Caffeine compared to 5.78 ± 2.11h for IR-Caffeine (p = 0.04189). However, total exposure was similar for SR-Caffeine and IR-Caffeine (90% CI: 89.89-120.50% to 94.49-123.82% for geometric least square mean of ln-transformed AUC0-t and AUC0-∞). In the Caff-VAS evaluation, the SR-Caffeine group showed significantly better scores for 'jitteriness', 'tiredness', 'alertness' and 'overall mood' for 8-12 h than the IR-Caffeine group. No adverse events were reported. Results demonstrated sustained release of caffeine over 24 h from SR-Caffeine as compared to IR-Caffeine, which showed significant improvements in the scores for 'relaxed', 'alertness' and 'overall mood' and significantly lower scores for the parameters-'jittery' and 'tired' for extended period.Clinical trial registration: CTRI/2021/06/034185.

Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives

For hundreds of years, mankind has been influencing its sleep and waking state through the adenosinergic system. For ~100 years now, systematic research has been performed, first started by testing the effects of different dosages of caffeine on sleep and waking behaviour. About 70 years ago, adenosine itself entered the picture as a possible ligand of the receptors where caffeine hooks on as an antagonist to reduce sleepiness. Since the scientific demonstration that this is indeed the case, progress has been fast. Today, adenosine is widely accepted as an endogenous sleep‐regulatory substance. In this review, we discuss the current state of the science in model organisms and humans on the working mechanisms of adenosine and caffeine on sleep. We critically investigate the evidence for a direct involvement in sleep homeostatic mechanisms and whether the effects of caffeine on sleep differ between acute intake and chronic consumption. In addition, we review the more recent evidence that adenosine levels may also influence the functioning of the circadian clock and address the question of whether sleep homeostasis and the circadian clock may interact through adenosinergic signalling. In the final section, we discuss the perspectives of possible clinical applications of the accumulated knowledge over the last century that may improve sleep‐related disorders. We conclude our review by highlighting some open questions that need to be answered, to better understand how adenosine and caffeine exactly regulate and influence sleep.

A novel bedtime pulsatile-release caffeine formula ameliorates sleep inertia symptoms immediately upon awakening

Sleep inertia is a disabling state of grogginess and impaired vigilance immediately upon awakening. The adenosine receptor antagonist, caffeine, is widely used to reduce sleep inertia symptoms, yet the initial, most severe impairments are hardly alleviated by post-awakening caffeine intake. To ameliorate this disabling state more potently, we developed an innovative, delayed, pulsatile-release caffeine formulation targeting an efficacious dose briefly before planned awakening. We comprehensively tested this formulation in two separate studies. First, we established the in vivo caffeine release profile in 10 young men. Subsequently, we investigated in placebo-controlled, double-blind, cross-over fashion the formulation's ability to improve sleep inertia in 22 sleep-restricted volunteers. Following oral administration of 160 mg caffeine at 22:30, we kept volunteers awake until 03:00, to increase sleep inertia symptoms upon scheduled awakening at 07:00. Immediately upon awakening, we quantified subjective state, psychomotor vigilance, cognitive performance, and followed the evolution of the cortisol awakening response. We also recorded standard polysomnography during nocturnal sleep and a 1-h nap opportunity at 08:00. Compared to placebo, the engineered caffeine formula accelerated the reaction time on the psychomotor vigilance task, increased positive and reduced negative affect scores, improved sleep inertia ratings, prolonged the cortisol awakening response, and delayed nap sleep latency one hour after scheduled awakening. Based on these findings, we conclude that this novel, pulsatile-release caffeine formulation facilitates the sleep-to-wake transition in sleep-restricted healthy adults. We propose that individuals suffering from disabling sleep inertia may benefit from this innovative approach.Trials registration: NCT04975360.

Acute caffeine intake in humans reduces post exercise performance in learning and memory

OBJECTIVE

To clarify the acute effect of caffeine on postexercise memory and learning performance.

METHODS

Eight male slow-to-normal caffeine metabolizers, unhabituated to caffeine, were recruited into this randomized, double blind, placebo controlled, cross over study. Caffeine (150 mg) or the placebo was consumed one hour prior to two 30 min submaximal cycling sessions. Blood was collected at the beginning, after 20 and 35 min of exercise and 30 min postexercise. Mature brain-derived neurotrophic factor (BDNF) and proBDNF concentrations were determined. Auditory memory was assessed immediately, 30 min and 24 h postexercise.

RESULTS

Participants averaged lower scores in every measure of learning and memory after ingesting caffeine compared to the placebo. Although the mean did not differ significantly for all measures, significant differences were found between the caffeine and placebo groups for the three indices; learning over time, short-term index and retroactive interference. The ratio of serum mBDNF:proBDNF increased with exercise across all time points. No significant difference in the mBDNF:proBDNF ratio was observed between treatment groups.

CONCLUSION

The consumption of caffeine prior to exercise may impair an unhabituated individual's capacity to learn and recall auditory information postexercise. However it is yet to be elucidated whether this is through caffeine's modulating effects on brain BDNF.

Applying principles of fatigue science to accident investigation: Transportation Safety Board of Canada (TSB) fatigue investigation methodology

Fatigue that is related to the amount and quality of sleep obtained can impair human performance in ways that can lead to accidents. As many transportation industries operate around the clock, fatigue and its effects cannot be eliminated completely; instead, they must be managed. A first step is to document the prevalence and role of fatigue in accidents that occur. The Transportation Safety Board of Canada (TSB) routinely investigates such transportation industry incidents to determine if fatigue was present, if it played a role, and if there were practices in place to effectively manage it and associated risks. Herein, we summarize and describe the TSB's fatigue investigation methodology in the hopes that investigators of other organizations and domains will find the concepts applicable to their operational context.

Sleep Deprivation and Racial Bias in the Decision to Shoot: A Diffusion Model Analysis

The current study examines the effect of sleep deprivation and caffeine use on racial bias in the decision to shoot. Participants deprived of sleep for 24 hr (vs. rested participants) made more errors in a shooting task and were more likely to shoot unarmed targets. A diffusion decision model analysis revealed sleep deprivation decreased participants’ ability to extract information from the stimuli, whereas caffeine impacted the threshold separation, reflecting decreased caution. Neither sleep deprivation nor caffeine moderated anti-Black racial bias in shooting decisions or at the process level. We discuss how our results clarify discrepancies in past work testing the impact of fatigue on racial bias in shooting decisions.

The impact of sleep deprivation and alcohol on driving: a comparative study

Background

There is concern about the detrimental effects of shift-workers’ increasing working hours particularly when driving sleep deprived. The approach to measuring the magnitude of driving impairment caused by sleep deprivation was by comparing it to alcohol. The study compared driving performance after 24-h of wakefulness to performance with a BrAC of just over 22 μg/100mls of breath which is equal to 50 mg of alcohol per 100mls of blood (Scottish drink-drive limit). The effectiveness of coffee as a countermeasure for driver fatigue and the association between subjective impairment and actual performance was also investigated.

Methods

A study of 30 participants (11 male and 19 female; mean age 21) was conducted. Subjects were tested under three conditions: fully rested, sleep deprived, and alcohol intoxicated – BrAC mean [SD] 25.95 μg [2.78]. Under each condition, subjects were tested before and after coffee ingestion. This involved driving simulation (Lane Change Task and Reaction Test) and subjective Likert scales (Karolinska Sleepiness Scale and driver impairment scale). Outcome measures included lane tracking adaptive mean deviation, reaction time, and subjective sleepiness and impairment ratings.

Results

Compared to alcohol, sleep deprived mean reaction times were slower (2.86 s vs. 2.34 s) and lateral control of the vehicle was reduced (lane tracking adaptive mean deviation: 0.5 vs. 0.3). Coffee did not produce an improvement when sleep deprived, and instead, performance deteriorated. Females were less impaired following sleep deprivation than males. Following prolonged wakefulness, the correlation between subjective impairment and actual performance was significant.

Conclusions

It was concluded that sleep deprivation has a greater impact on driving performance than a BrAC of 22 μg/100mls of breath, as measured by driving simulation. Coffee is not an effective countermeasure for sleep deprived driving and drivers’ ability to judge this impairment is suggested to be limited.

The Influence of Sleep Quality, Vigilance, and Sleepiness on Driving-Related Cognitive Abilities: A Comparison between Young and Older Adults

Background: Driving performance is strongly vulnerable to drowsiness and vigilance fluctuations. Excessive sleepiness may alter concentration, alertness, and reaction times. As people age, sleep undergoes some changes, becoming fragmented and less deep. However, the effects of these modifications on daily life have not been sufficiently investigated. Recently, the assessment of sleepiness became mandatory in Europe for people at risk who need the driving license release. Moreover, considering the expectation that people around the world are rapidly aging, it is necessary to investigate the relationships between senescence sleep changes, vigilance levels, and driving-related cognitive skills. Method: 80 healthy subjects (40 young adults and 40 elders) participated in the study. Sleep quality, sleepiness, and vigilance levels were assessed through the Pittsburgh Sleep Quality Index, the Karolinska Sleepiness Scale, the Epworth Sleepiness Scale, and the Psychomotor Vigilance Task (PVT). Driving-related cognitive abilities were assessed through Vienna Test System TRAFFIC, investigating selective attention, tachistoscopic perception, and risk assumption. Results: 2 × 2 between-subject ANOVAs showed less habitual sleep efficiency and worse performances in PVT in the older group. Unexpectedly, younger subjects show higher self-rated sleepiness. Moreover, older adults have lower performance in attention and perception tests, but they appear to be more cautious in situations involving traffic. Finally, the multiple regressions show age to be the only robust predictor of cognitive driving-related abilities. Conclusions: This is the first study that investigates the relationships among sleepiness/vigilance and specific driving-related cognitive skills on a sufficiently large sample. Nevertheless, the study should be considered preliminary and does not allow us to understand how specific changes in sleep architecture impact performances in the elders' everyday life and, specifically, on driving skills.

Caffeine as an adulterant of coca paste seized samples: preclinical study on the rat sleep-wake cycle

Caffeine is a common active adulterant found in illicit drugs of abuse, including coca paste (CP). CP is a smokable form of cocaine mainly consumed in South America, produced during the cocaine-extraction process. CP has high abuse liability and its chronic consumption induces severe sleep-wake alterations. However, the effect of CP on the sleep-wake cycle and the effect of the presence of caffeine as an adulterant remain unknown. We studied the effect of an acute intraperitoneal injection of 2.5 and 5 mg/kg of a representative CP sample adulterated with caffeine (CP1) on the rat sleep-wake cycle. Compared with saline, administration of CP1 induced an increase in wakefulness and a decrease in light (light sleep) and slow wave sleep that was larger than the effects produced by equivalent doses of cocaine. Compared with CP1, combined treatment with cocaine (5 mg/kg) and caffeine (2.5 mg/kg), a surrogate of CP1, elicited similar effects. In contrast, a nonadulterated CP sample (CP2) produced an effect that was not different from cocaine. Our data indicate that caffeine produces a significant potentiation of the wakefulness-promoting effect of cocaine, suggesting that caffeine should be explored as a causal agent of clinical symptoms observed in CP users.

Caffeine to optimize cognitive function for military mission-readiness: a systematic review and recommendations for the field

Context

In 2001 the Institute of Medicine (IOM) released a report on the use of caffeine during sustained military operations in which recommendations for research and practice were made.

Objective

This systematic review serves as an update on the current quality of the evidence and addresses gaps in the current literature surrounding the effects of caffeinated foods and beverages on cognitive functioning in healthy adult populations exposed to military-like moderators.

Data Sources

PubMed, CINAHL, Embase, PsycInfo, and the Cochrane Library were searched.

Study Selection

Peer-reviewed randomized controlled trials published in the English language since 1998 were eligible.

Data Extraction

Twenty-five trials were included and assessed for methodological quality, and descriptive data were extracted according to each military-like moderator identified.

Data Synthesis

Moderators included sleep deprivation (n = 17), physical or mental exertion (n = 4), sleep deprivation combined with a sustained military operation (n = 3), and physical exertion combined with low ambient temperature (n = 1).

Conclusions

The effects of caffeine supplementation on cognitive functioning in sleep-deprived subjects included improvements in attention and vigilance, complex reaction time, and problem solving and reasoning in the trials reviewed. These findings are consistent with the conclusions reached in the 2001 IOM report. This review contributes to the field by addressing gaps outlined in the IOM report.

Sensorimotor and executive function slowing in anesthesiology residents after overnight shifts

STUDY OBJECTIVE

Medical residents working overnight call shifts experience sleep deprivation and circadian clock disruption. This leads to deficits in sensorimotor function and increases in workplace accidents. Using quick tablet-based tasks, we investigate whether measureable executive function differences exist following a single overnight call versus routine shift, and whether factors like stress, rest and caffeine affect these measures.

DESIGN

A prospective, observational, longitudinal, comparison study was conducted.

SETTING

An academic tertiary hospital's main operating room suite staffed by attending anesthesiologists, anesthesiology residents, anesthesiologist assistants and nurse anesthetists.

PATIENTS

Subjects were 30 anesthesiology residents working daytime shifts and 30 peers working overnight call shifts from the University of Texas Health Science Center at Houston.

INTERVENTIONS

Before and after their respective work shifts, residents completed the Stanford Sleepiness Scale (SSS) and the ProPoint and AntiPoint tablet-based tasks. These latter tasks are designed to measure sensorimotor and executive functions, respectively.

MEASUREMENTS

The SSS is a self-reported measure of sleepiness. Response times (RTs) are measured in the pointing tasks.

MAIN RESULTS

Call residents exhibited increased RTs across their shifts (post-pre) on both ProPoint (p=0.002) and AntiPoint (p<0.002) tasks, when compared to Routine residents. Increased stress was associated with decreases in AntiPoint RT for Routine (p=0.007), but with greater increases in sleepiness for Call residents (p<0.001). Further, whether or not a Call resident consumed caffeine habitually was associated with ProPoint RT changes; with Call residents who habitually drink caffeine having a greater Pre-Post difference (i.e., more slowing, p<0.001) in ProPoint RT.

CONCLUSIONS

These results indicate that (1) overnight Call residents demonstrate both sensorimotor and cognitive slowing compared to routine daytime shift residents, (2) sensorimotor slowing is greater in overnight Call residents who drink caffeine habitually, and (3) increased stress during a shift reduces (improves) cognitive RTs during routine daytime but not overnight call shifts.

Effects of total sleep deprivation on divided attention performance

Dividing attention across two tasks performed simultaneously usually results in impaired performance on one or both tasks. Most studies have found no difference in the dual-task cost of dividing attention in rested and sleep-deprived states. We hypothesized that, for a divided attention task that is highly cognitively-demanding, performance would show greater impairment during exposure to sleep deprivation. A group of 30 healthy males aged 21-30 years was exposed to 40 h of continuous wakefulness in a laboratory setting. Every 2 h, subjects completed a divided attention task comprising 3 blocks in which an auditory Go/No-Go task was 1) performed alone (single task); 2) performed simultaneously with a visual Go/No-Go task (dual task); and 3) performed simultaneously with both a visual Go/No-Go task and a visually-guided motor tracking task (triple task). Performance on all tasks showed substantial deterioration during exposure to sleep deprivation. A significant interaction was observed between task load and time since wake on auditory Go/No-Go task performance, with greater impairment in response times and accuracy during extended wakefulness. Our results suggest that the ability to divide attention between multiple tasks is impaired during exposure to sleep deprivation. These findings have potential implications for occupations that require multi-tasking combined with long work hours and exposure to sleep loss.

Prevention of fatigue and insomnia in shift workers-a review of non-pharmacological measures

Background

Excessive fatigue and insomnia are common among shift workers and can lead to negative effects such as reduced work performance, processing errors, accidents at work, absenteeism, reduced quality of life, and symptoms of depression. Moreover, work in rotating shifts can be a risk factor for different somatic and psychiatric diseases and may contribute to poor health, especially in elder adults and women. This review aims to show non-pharmacological preventive measures against fatigue and insomnia in shift workers.

Method

Computerized literature searches in MedLine and in the Cochrane Library were performed with the following key words: shift work disorder, fatigue, insomnia, shift work, measures, treatment, therapy, strategies and coping. The search was limited to non-pharmacological studies that were conducted on human subjects and published as English-language articles in peer-reviewed journals since 1970. Additional studies were identified through the reference sections of relevant articles. Eighteen articles on fatigue in shift workers, including six original research articles with a total sample size of 3504 probands consisting of industrial workers, office employees, aircraft maintenance engineers, and non-shift workers working in simulated shifts, were analyzed, as well as seven articles on insomnia, including an original research article with a sample size of 26 media workers. Also, 4 reviews on shift work disorder were analyzed.

Main

The occurrence of fatigue and insomnia in shift workers associated with a working period is described as shift work disorder. Estimations on the prevalence of shift work disorder in shift workers vary between 5 % and about 20 %; about one in three shift workers is affected by insomnia and up to 90 % of shift workers report regular fatigue and sleepiness at the workplace. We concluded that there is a necessity for treatments to improve the sleep quality of the shift working population. The most common non-pharmacological recommendations to improve sleep quality and to reduce insomnia and fatigue were scheduling, bright light exposure, napping, psychoeducation for sleep hygiene, and cognitive-behavioral measures.

Conclusion

Some important preventive coping strategies for fatigue associated with shift work such as napping and exposure to bright light have already been investigated and are generally approved. A few studies also provide good evidence for the efficacy of cognitive-behavioral techniques in the treatment of chronic primary and comorbid insomnia. These coping strategies summarized in this paper should be considered in the workplace health promotion programs of each work environment to improve working conditions for shift workers and to save money.

Benefits of Sleep Extension on Sustained Attention and Sleep Pressure Before and During Total Sleep Deprivation and Recovery

OBJECTIVES

To investigate the effects of 6 nights of sleep extension on sustained attention and sleep pressure before and during total sleep deprivation and after a subsequent recovery sleep.

DESIGN

Subjects participated in two experimental conditions (randomized cross-over design): extended sleep (EXT, 9.8 ± 0.1 h (mean ± SE) time in bed) and habitual sleep (HAB, 8.2 ± 0.1 h time in bed). In each condition, subjects performed two consecutive phases: (1) 6 nights of either EXT or HAB (2) three days in-laboratory: baseline, total sleep deprivation and after 10 h of recovery sleep.

SETTING

Residential sleep extension and sleep performance laboratory (continuous polysomnographic recording).

PARTICIPANTS

14 healthy men (age range: 26-37 years).

INTERVENTIONS

EXT vs. HAB sleep durations prior to total sleep deprivation.

MEASUREMENTS AND RESULTS

Total sleep time and duration of all sleep stages during the 6 nights were significantly higher in EXT than HAB. EXT improved psychomotor vigilance task performance (PVT, both fewer lapses and faster speed) and reduced sleep pressure as evidenced by longer multiple sleep latencies (MSLT) at baseline compared to HAB. EXT limited PVT lapses and the number of involuntary microsleeps during total sleep deprivation. Differences in PVT lapses and speed and MSLT at baseline were maintained after one night of recovery sleep.

CONCLUSION

Six nights of extended sleep improve sustained attention and reduce sleep pressure. Sleep extension also protects against psychomotor vigilance task lapses and microsleep degradation during total sleep deprivation. These beneficial effects persist after one night of recovery sleep.

Acute stress blocks the caffeine-induced enhancement of contextual memory retrieval in mice

This study investigated in mice the dose-effect of caffeine on memory retrieval in non-stress and stress conditions. C57 Bl/6 Jico mice learned two consecutive discriminations (D1 and D2) in a four-hole board which involved either distinct contextual (CSD) or similar contextual (SSD) cues. All mice received an i.p. injection of vehicle or caffeine (8, 16 or 32mg/kg) 30min before the test session. Results showed that in non-stress conditions, the 16mg/kg caffeine dose induced a significant enhancement of D1 performance in CSD but not in SSD. Hence, we studied the effect of an acute stress (electric footshocks) administered 15min before the test session on D1 performance in caffeine-treated mice. Results showed that stress significantly decreased D1 performance in vehicle-treated controls and the memory-enhancing effect induced by the 16mg/kg caffeine dose in non-stress condition is no longer observed. Interestingly, whereas caffeine-treated mice exhibited weaker concentrations of plasma corticosterone as compared to vehicles in non-stress condition, stress significantly increased plasma corticosterone concentrations in caffeine-treated mice which reached similar level to that of controls. Overall, the acute stress blocked both the endocrinological and memory retrieval enhancing effects of caffeine.

Caffeine does not entrain the circadian clock but improves daytime alertness in blind patients with non-24-hour rhythms

•

Most totally blind individuals have Non-24-Hour Sleep–Wake Disorder (N24HSWD).

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Optimal treatment should reset the underlying non-entrained circadian pacemaker.

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We tested daily caffeine treatment (150 mg, 10 a.m.) in three blind patients with N24HSWD.

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Caffeine treatment improved daytime alertness at adverse circadian phases.

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Caffeine treatment was unable to entrain the circadian clock.

Objective/Background

Totally blind individuals are highly likely to suffer from Non-24-Hour Sleep-Wake Disorder due to a failure of light to reset the circadian pacemaker in the suprachiasmatic nuclei. In this outpatient case series, we investigated whether daily caffeine administration could entrain the circadian pacemaker in non-entrained blind patients to alleviate symptoms of non-24-hour sleep–wake disorder.

Patients/Methods

Three totally blind males (63.0 ± 7.5 years old) were studied at home over ~4 months. Urinary 6-sulphatoxymelatonin (aMT6s) rhythms were measured for 48 h every 1–2 weeks. Participants completed daily sleep–wake logs, and rated their alertness and mood using nine-point scales every ~2–4 h while awake on urine sampling days. Caffeine capsules (150 mg per os) were self-administered daily at 10 a.m. for approximately one circadian beat cycle based on each participant's endogenous circadian period τ and compared to placebo (n = 2) or no treatment (n = 1) in a single-masked manner.

Results

Non-24-h aMT6s rhythms were confirmed in all three participants (τ range = 24.32–24.57 h). Daily administration of 150 mg caffeine did not entrain the circadian clock. Caffeine treatment significantly improved daytime alertness at adverse circadian phases (p < 0.0001) but did not decrease the occurrence of daytime naps compared with placebo.

Conclusions

Although caffeine was able to improve daytime alertness acutely and may therefore provide temporary symptomatic relief, the inability of caffeine to correct the underlying circadian disorder means that an entraining agent is required to treat Non-24-Hour Sleep–Wake Disorder in the blind appropriately.

Caffeine improves reaction time, vigilance and logical reasoning during extended periods with restricted opportunities for sleep

RATIONALE

Various occupational groups are required to maintain optimal physical and cognitive function during overnight periods of wakefulness, often with less than optimal sleep. Strategies are required to help mitigate the impairments in cognitive function to help sustain workplace safety and productivity.

OBJECTIVES

To test the effectiveness of repeated 200 mg doses of caffeine on cognitive function and live-fire marksmanship with soldiers during three successive nights of sustained wakefulness followed by 4-h afternoon sleep periods.

METHODS

Twenty Special Forces personnel (28.6 ± 4.7 years, 177.6 ± 7.5 cm and 81.2 ± 8.0 kg) were randomly assigned to receive four 200-mg doses of caffeine (n = 10) or placebo (n = 10) during the late evening and early morning hours during three successive days. An afternoon 4-h sleep period followed. The psychomotor (PVT) and field (FVT) vigilance, logical reasoning (LRT) tests and a vigilance monitor assessed cognitive function throughout the study. Live-fire marksmanship requiring friend-foe discrimination was assessed.

RESULTS

Caffeine maintained speed on the PVT (p < 0.02), improved detection of events during FVT (p < 0.001), increased number of correct responses to stimuli as assessed by the vigilance monitor (p < 0.001) and increased response speed during the LRT (p < 0.001) throughout the three overnight testing periods. Live-fire marksmanship was not altered by caffeine.

CONCLUSIONS

A total daily dose of 800 mg caffeine during successive overnight periods of wakefulness is an effective strategy to maintain cognitive function when optimal sleep periods during the day are not available.

Effects of 28-days ingestion of a slow-release energy supplement versus placebo on hematological and cardiovascular measures of health

Background

Recently, slow release tablets have been developed to prolong energy release throughout the day. The efficacy of the delivery of slow-release caffeine alone is fairly well documented; however, an assessment of safety and tolerability of prolonged use of slow-release energy supplements is lacking. Therefore the objective of this study was to investigate the effect of daily ingestion of a slow-release energy supplement for 28 days on blood chemistry and resting cardiovascular measures in healthy men and women.

Methods

Forty healthy individuals (20 males, 20 females; age: 22.73 ± 3.06 years; height: 171.68 ± 10.45 cm; mass: 74.49 ± 15.51 kg; BMI: 25.08 ± 3.66 (kg • m²) ^-1) participated in this randomized, double-blind, placebo controlled study. Following a 12-hour fast, participants reported for pre-testing. Testing consisted of resting heart rate (RHR) and blood pressure (BP) measures, followed by assessment of metabolic blood chemistry, blood lipids and complete cell counts. Participants then supplemented with either Energize™ (SUPP) or placebo (PL) for 28 days. Post-testing occurred 24-hours after ingestion of the final dose and consisted of the same protocol at the same time of day as pre-testing.

Results

No significant changes in outcome measures were observed. A significant difference between groups was observed for plasma glucose concentrations; however, follow-up testing revealed that pre- to post-supplementation changes were not significant for either SUPP or PL. All variables remained within normal adult reference ranges. No adverse events were reported.

Conclusions

These findings indicate that 28 consecutive days ingestion of a slow release energy supplement containing caffeine in caffeine users is both safe and tolerable.

Cumulative neurobehavioral and physiological effects of chronic caffeine intake: individual differences and implications for the use of caffeinated energy products

The use of caffeine-containing energy products has increased worldwide in recent years. All of the top-selling energy drinks contain caffeine, which is likely to be the primary psychoactive ingredient in these products. Research shows that caffeine-containing energy products can improve cognitive and physical performance. Presumably, individuals consume caffeine-containing energy products to counteract feelings of low energy in situations causing tiredness, fatigue, and/or reduced alertness. This review discusses the scientific evidence for sleep loss, circadian phase, sleep inertia, and the time-on-task effect as causes of low energy and summarizes research assessing the efficacy of caffeine to counteract decreased alertness and increased fatigue in such situations. The results of a placebo-controlled experiment in healthy adults who had 3 nights of total sleep deprivation (with or without 2-hour naps every 12 hours) are presented to illustrate the physiological and neurobehavioral effects of sustained low-dose caffeine. Individual differences, including genetic factors, in the response to caffeine and to sleep loss are discussed. The review concludes with future directions for research on this important and evolving topic.

Pharmacological interventions for sleepiness and sleep disturbances caused by shift work

BACKGROUND

Shift work results in sleep-wake disturbances, which cause sleepiness during night shifts and reduce sleep length and quality in daytime sleep after the night shift. In its serious form it is also called shift work sleep disorder. Various pharmacological products are used to ameliorate symptoms of sleepiness or poor sleep length and quality.

OBJECTIVES

To evaluate the effects of pharmacological interventions to reduce sleepiness or to improve alertness at work and decrease sleep disturbances whilst off work, or both, in workers undertaking shift work in their present job and to assess their cost-effectiveness.

SEARCH METHODS

We searched CENTRAL, MEDLINE, EMBASE, PubMed and PsycINFO up to 20 September 2013 and ClinicalTrials.gov up to July 2013. We also screened reference lists of included trials and relevant reviews.

SELECTION CRITERIA

We included all eligible randomised controlled trials (RCTs), including cross-over RCTs, of pharmacological products among workers who were engaged in shift work (including night shifts) in their present jobs and who may or may not have had sleep problems. Primary outcomes were sleep length and sleep quality while off work, alertness and sleepiness, or fatigue at work.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies, extracted data and assessed risk of bias in included trials. We performed meta-analyses where appropriate.

MAIN RESULTS

We included 15 randomised placebo-controlled trials with 718 participants. Nine trials evaluated the effect of melatonin and two the effect of hypnotics for improving sleep problems. One trial assessed the effect of modafinil, two of armodafinil and one examined caffeine plus naps to decrease sleepiness or to increase alertness.Melatonin (1 to 10 mg) after the night shift may increase sleep length during daytime sleep (mean difference (MD) 24 minutes, 95% confidence interval (CI) 9.8 to 38.9; seven trials, 263 participants, low quality evidence) and night-time sleep (MD 17 minutes, 95% CI 3.71 to 30.22; three trials, 234 participants, low quality evidence) compared to placebo. We did not find a dose-response effect. Melatonin may lead to similar sleep latency times as placebo (MD 0.37minutes, 95% CI - 1.55 to 2.29; five trials, 74 participants, low quality evidence).Hypnotic medication, zopiclone, did not result in significantly longer daytime sleep length compared to placebo in one low quality trial and we could not use the data from the study on lormetazepam.Armodafinil taken before the night shift probably reduces sleepiness by one point on the Karolinska Sleepiness Scale (KSS) (MD -0.99, 95% CI -1.32 to -0.67; range 1 to 10; two trials, 572 participants, moderate quality evidence) and increases alertness by 50 ms in a simple reaction time test (MD -50.0, 95% CI -85.5 to -15.5) at three months' follow-up in shift work sleep disorder patients. Modafinil probably has similar effects on sleepiness (KSS) (MD -0.90, 95% CI -1.45 to -0.35; one trial, 183 participants, moderate quality evidence) and alertness in the psychomotor vigilance test in the same patient group. Post-marketing, severe skin reactions have been reported. Adverse effects reported by trial participants were headache, nausea and a rise in blood pressure. There were no trials in non-patient shift workers.Based on one trial, caffeine plus pre-shift naps taken before the night shift decreased sleepiness (KSS) (MD -0.63, 95% CI -1.09 to -0.17).We judged most trials to have a low risk of bias even though the randomisation method and allocation concealment were often not described.

AUTHORS' CONCLUSIONS

There is low quality evidence that melatonin improves sleep length after a night shift but not other sleep quality parameters. Both modafinil and armodafinil increase alertness and reduce sleepiness to some extent in employees who suffer from shift work sleep disorder but they are associated with adverse events. Caffeine plus naps reduces sleepiness during the night shift, but the quality of evidence is low. Based on one low quality trial, hypnotics did not improve sleep length and quality after a night shift.We need more and better quality trials on the beneficial and adverse effects and costs of all pharmacological agents that induce sleep or promote alertness in shift workers both with and without a diagnosis of shift work sleep disorder. We also need systematic reviews of their adverse effects.

Working memory performance of older adults with insomnia

Older individuals suffering insomnia typically report declines in their cognitive performance beyond what they consider to be normal changes due to the aging process. Recent neuro-imaging studies have demonstrated frontal lobe hypo-activation among insomniac populations when compared with healthy, good sleepers. However, research is yet to confirm whether frontal lobe hypo-activation translates into objective declines when performing tasks hypothesized to draw upon this brain region. This study aimed to investigate whether older insomnia sufferers demonstrate significantly impaired performance on a challenging working memory task when compared with age-matched good sleepers. Forty-nine older individuals (mean age = 69.43 years, SD = 4.83) suffering from sleep maintenance insomnia were compared with 49 age-matched good sleepers. Cognitive performance was assessed using the Double Span Memory Task, a computer-based working memory task that requires participants to indicate the names and/or spatial locations of increasingly longer sequences of visually presented objects. After controlling for general intelligence, the individuals suffering from insomnia did not perform differently when compared with the good sleepers on either the simpler or more cognitively demanding components of the task. Older individuals with insomnia did not display an observable impairment of working memory in this study relative to good sleepers. Despite the mixed results from previous research, this study adds weight to the absence of objective impairment in insomniacs, at least while performing short-term demanding cognitive tasks.

Working in our sleep

A large body of sleep physiology research highlights a broad array of effects of sleep on human functioning. Until recently, this literature has been completely isolated from the organizational psychology literature. The purpose of this paper is to further extend the sleep literature into the organizational psychology literature, with a focus on self-regulation in the workplace. I summarize the sleep literature into a model of sleep self-regulation. Next, I highlight initial research in organizational psychology which has drawn from basic sleep physiology research. Following this, I generate new propositions linking sleep to work withdrawal, goal level, incivility, and defection in workplace social dilemmas. Finally, I close with a discussion of methods for conducting sleep research in organizational psychology, as well as some promising areas for future research.

Motor activity in depressed patients during therapeutic sleep deprivation

PROBLEM

Both sleep and motor activity have a bidirectional relationship with depression. The existing literature on motor activity during therapeutic sleep deprivation in depressed patients is inconsistent and fragmentary. In the present study we measured motor activity continuously during 40 hours of sleep deprivation in depressed patients.

METHOD

Thirty-four inpatients suffering from a major depression (DSM-IV) underwent sleep deprivation with a continuous waking period of 40 hours. Motor activity of the patients was continuously recorded using an actigraph on the non-dominant wrist. The effect of sleep deprivation was assessed by the Hamilton Depression Scale (six-item version), thus separating the group into responders and non-responders to sleep deprivation.

RESULTS

We found no significant differences in motor activity between responders and non-responders on the day before sleep deprivation. During the night, responders to sleep deprivation exhibited a higher motor activity and less periods of rest. On the day after sleep deprivation, responders exhibited a higher activity, too.

CONCLUSIONS

Motor activity levels differ between the two groups, thus giving more insight into possible mechanisms of action of the therapeutic sleep deprivation. We suggest that higher motor activity during the night prevents naps and leads to better response to sleep deprivation.

Cognitive Performance during Sustained Wakefulness: A Low Dose of Caffeine Is Equally Effective as Modafinil in Alleviating the Nocturnal Decline

Cognitive performance at night exhibits a substantial drop, typically before dawn. One of the means of dealing with this phenomenon, as well as with the accompanying sleepiness during sustained wakefulness, is the administration of stimulants. The most widely used and well-documented stimulants are caffeine, amphetamines, and modafinil. Of these, amphetamines are the least recommended, as they may severely affect behavior. Caffeine and modafinil seem to produce relatively milder side effects and usually only at high doses. Previous comparison studies have revealed equal efficacy of both the stimulants in maintaining alertness and performance during sustained wakefulness. However, these studies used relatively high, and thus not completely safe, doses of these drugs (600 mg caffeine and 400 mg modafinil). Therefore, the aim of the present study was to assess the efficacy of a low and medically safe dose of caffeine (200 mg) and modafinil (200 mg) in maintaining cognitive performance during sustained wakefulness. A flight simulation task was chosen for the assessment of the stimulants in a counter-balanced, within-subject design under four different conditions: baseline (no drugs), placebo, caffeine (200 mg), and modafinil (200 mg). The equal effectiveness of both drugs in abolishing the nocturnal drop in cognitive performance, as well as of oral temperature and blood pressure, supported the use of low doses of caffeine and modafinil for the maintenance of alertness in healthy subjects during sustained wakefulness.

Vigilance Levels During and After Bright Light Exposure in the First Half of the Night

Fourteen healthy subjects (8 women, 6 men, aged 22-35 yr) were recruited. Each subject was exposed, in a counterbalanced order, to bright white light (BWL: 3000 lux) and to dim red light (DRL: <15 lux) at a 1-week interval. Light treatments were administered from 00:30 to 04:30 h during sleep deprivation. Salivary melatonin and urinary cortisol concentrations were measured as was core body temperature. Vigilance levels were evaluated by subjective estimates, maintenance of wakefulness tests (MWT), waking EEG recordings, and three performance tests. Under BWL melatonin secretion was suppressed and core body temperature was significantly higher than under DRL. The BWL and DRL conditions produced no difference in cortisol secretion. Significant effects of BWL treatment were found for the MWT and theta-alpha and beta-1 frequency bands of the waking EEG. There was no significant effect of BWL on subjective alertness and performance. Vigilance measures were similar under the two conditions for the tests performed 1.5 h after the end of light treatments. Overall, the findings suggest that bright light (BL) exposure in the first half of the night decreases EEG-defined sleep propensity but has only modest effects on other aspects of vigilance.

Suppression of hippocampal cell proliferation by short-term stimulant drug administration in adult rats

Sleep loss is known to potently suppress adult hippocampal cell proliferation and neurogenesis. Whether sleep suppression following acute administration of stimulant drugs also decreases hippocampal cell proliferation is not known. The present study examined the effect of three mechanistically distinct stimulants (caffeine, methamphetamine and modafinil) on cell proliferation. To maximize sleep suppression, these drugs were administered to rats (three i.p. injections, once every 4 h) during their sleep period (i.e. 12-h light phase). At the end of the light phase, 5-bromo-2'-deoxyuridine (200 mg/kg, i.p.) was injected and animals were killed 2 h later. Polygraphic recordings and locomotor activity measurements confirmed the wake-promoting and sleep-suppressing actions of each treatment. Results indicate that caffeine (20 mg/kg), methamphetamine (1.5 mg/kg) and modafinil (300 mg/kg) differentially suppressed sleep (45-91%) and selectively reduced cell proliferation in the hilus (12-44%), these results being significant for both caffeine and modafinil. When the same experiment was repeated in the dark (active) phase, the suppressant effect on hippocampal cell proliferation was either absent or greatly attenuated. In a further experiment, the effect of acute modafinil treatment in the light phase was shown to persist for 3 weeks after BrdU administration. We hypothesize that the differential effect of the stimulant drugs in the light vs. dark phase is attributable primarily to sleep suppression in the light. As abuse of stimulant drugs invariably leads to disrupted sleep in humans, our results suggest that they may, at least in part, decrease hippocampal neurogenesis via sleep loss and thereby adversely affect hippocampal-dependent processes.

Dolphins maintain cognitive performance during 72 to 120 hours of continuous auditory vigilance

The present study reports the first use of a choice visual–vocal response time cognitive task, during 72 or 120 h of continuous auditory vigilance. Two adult bottlenose dolphins (Tursiops truncatus), NAY(male) and SAY (female), maintained a very high detection rate(91.1–98.7%) of random 1.5 s goal tones infrequently substituted in a background of frequent 0.5 s equal-amplitude tones over continuous 72 or 120 h sessions. In addition, a choice visual–vocal response time task (CVVRT)tested cognitive performance during night time sessions, when the dolphins would have ordinarily been resting or asleep as we had observed in previous studies. NAY and SAY detected a single-bar, posterior, vertical, green (S1g)or 3-bar, anterior, horizontal, red (S2r) LED light stimulus presented randomly to each eye. They responded with a different vocalization (whistle or pulse burst) to each stimulus (S1g or S2r) presented randomly to left and right eyes. The animals maintained high levels of goal tone detection without signs of sleep deprivation as indicated by behavior, blood indices or marked sleep rebound during 24 h of continuous post-experiment observation. Acoustic goal tone response time (AGTRT) overall did not change during the 72 h(F=0.528, P=0.655) or 120 h (F=0.384, P=0.816) sessions. Nor did CVVRT slow or degrade over the 72 h(F=4.188, P=0.104) or 120 h (F=2.298, P=0.119) AGTRT sessions.

Clinical management of jet lag: what can be proposed when performance is critical?

Jet lag, which appears after a long lasting transmeridian flight, is generally considered as a consequence of a desynchronization of circadian rhythms. After a recall of the circadian physiology, a modern view of the physiopathology is proposed. The major idea that emerges from these data is that only the wake-sleep rhythm may adapt itself quickly during jet lag and therefore it constitutes a good therapeutic target for physicians. We focus on the modalities of a light pharmacological aid to counteract jet lag. This punctual aid should help passengers to restore an adapted wake-sleep rhythm as quickly as possible. From this point of view, hypnotics may constitute a good indication. Finally, we suggest that the use of psychostimulants could also be interesting in very exceptional circumstances.

Effects of caffeine on alertness as measured by infrared reflectance oculography

RATIONALE

Caffeine is a well-known stimulant that can be used to increase alertness and performance especially in low arousal situations such as monotonous highway driving or after sleep deprivation. The effects of caffeine in rested, alert, participants are less clear, and this may be attributable to difficulties in objectively assessing small changes in alertness.

OBJECTIVES

The present study examined the effects of caffeine in non-sleep-deprived participants with methods that have previously been shown to be sensitive to changes in alertness. In order to avoid confounding results, low, or non-users of caffeine, were sought as participants.

MATERIALS AND METHODS

Twelve subjects participated in a within-subjects double-blind placebo-controlled design study and were administered either a capsule containing 200 mg of caffeine or placebo on two separate days. Ten-minute long tests of vigilance were performed at baseline and then at 30, 60, 120, 180, and 240 min after swallowing the capsule. During vigilance tests, eye blink variables were measured using infrared reflectance oculography and converted into a drowsiness score, Johns Drowsiness Scale (JDS).

RESULTS

Caffeine significantly reduced JDS scores (drowsiness) and reaction times, and these changes persisted for 3 to 4 h. Self reports of sleepiness were not as sensitive, with Karolinska Sleepiness Scale scores only being significantly lower in the caffeine compared to placebo condition at 30 min post capsule administration.

CONCLUSIONS

The results demonstrated that despite being well rested, administration of caffeine significantly increased alertness and enhanced performance, and these changes were able to be detected with the JDS.

Sleep deprivation and vigilant attention

Sleep deprivation severely compromises the ability of human beings to respond to stimuli in a timely fashion. These deficits have been attributed in large part to failures of vigilant attention, which many theorists believe forms the bedrock of the other more complex components of cognition. One of the leading paradigms used as an assay of vigilant attention is the psychomotor vigilance test (PVT), a high signal-load reaction-time test that is extremely sensitive to sleep deprivation. Over the last twenty years, four dominant findings have emerged from the use of this paradigm. First, sleep deprivation results in an overall slowing of responses. Second, sleep deprivation increases the propensity of individuals to lapse for lengthy periods (>500 ms), as well as make errors of commission. Third, sleep deprivation enhances the time-on-task effect within each test bout. Finally, PVT results during extended periods of wakefulness reveal the presence of interacting circadian and homeostatic sleep drives. A theme that links these findings is the interplay of "top-down" and "bottom-up" attention in producing the unstable and unpredictable patterns of behavior that are the hallmark of the sleep-deprived state.

Effects of dextroamphetamine, caffeine and modafinil on psychomotor vigilance test performance after 44 h of continuous wakefulness

Prolonged sleep loss impairs alertness, vigilance and some higher-order cognitive and affective capacities. Some deficits can be temporarily reversed by stimulant medications including caffeine, dextroamphetamine, and modafinil. To date, only one study has directly compared the effectiveness of these three compounds and specified the doses at which all were equally effective in restoring alertness and vigilance following 64 h of wakefulness. The present study compared the effectiveness of these same three stimulants/doses following a less extreme period of sleep loss (i.e., 44 h). Fifty-three healthy adults received a single dose of modafinil 400 mg (n = 11), dextroamphetamine 20 mg (n = 16), caffeine 600 mg (n = 12), or placebo (n = 14) after 44 h of continuous wakefulness. After 61 h of being awake, participants obtained 12 h of recovery sleep. Psychomotor vigilance was assessed bi-hourly during waking and following recovery sleep. Relative to placebo, all three stimulants were equally effective in restoring psychomotor vigilance test speed and reducing lapses, although the duration of action was shortest for caffeine and longest for dextroamphetamine. At these doses, caffeine was associated with the highest percentage of subjectively reported side-effects while modafinil did not differ significantly from placebo. Subsequent recovery sleep was adversely affected in the dextroamphetamine group, but none of the stimulants had deleterious effects on postrecovery performance. Decisions regarding stimulant selection should be made with consideration of how factors such as duration of action, potential side-effects, and subsequent disruption of recovery sleep may interact with the demands of a particular operational environment.

Changes in sensitivity of response distributions to changing reinforcement ratios during exposure to ephedrine, caffeine, and ephedrine-caffeine combinations

Changes in the sensitivity of response distributions to changes in reward distribution (reinforcer distribution sensitivity) were examined when rats were exposed to low and moderate doses of caffeine, ephedrine, and caffeine-ephedrine combinations. The data show significant decreases in sensitivity in response distributions to changes in reward schedule values during exposure to caffeine and ephedrine/caffeine combinations, whereas ephedrine alone resulted in overmatching comparable with baseline and NaCl conditions. Rats treated either with 3.0-mg/kg or 10.0-mg/kg doses of caffeine and all combinations of ephedrine at doses of 1.8 or 5.6 mg/kg with caffeine at 3.0 or 10.0 mg/kg showed reduced sensitivity in response distributions to differences in reinforcement schedule ratios. In contrast, when rats were exposed to ephedrine at 1.8 or 5.6 mg/kg, they maintained or increased the degree of overmatching. Although reinforcer distribution sensitivity was altered, drug exposure did not significantly affect the absolute rates of responding. Bias varied after exposure to caffeine, ephedrine, and their combinations, but not systematically. Finally, whereas the estimates of goodness of fit (r2) to the matching equation showed some decreases during drug exposure, these were neither statistically significant nor correlated with drug dose. These results suggest differential effects of ephedrine and caffeine on the sensitivity of response distributions to changes in reinforcement ratio distributions, with deleterious effects of caffeine and ephedrine/caffeine combinations.

[Pharmacological approach to desychronization of the sleep-wakefulness cycle in the military and sport environment]

Sports and military environments have many common features - intense physical activity, rigorous physical environment (heat, cold, high or low pressure, hypoxia, acceleration...), specific psychosocial atmosphere, team spirit. If combined with jet lag syndrome, these specific conditions can favor altered physical and mental performance. There is always the temptation to use drugs as a simple way to reduce the penalizing effects. The available compounds known to affect sleep and wakefulness include hypnotics, benzodiazepines and non benzodiazepines such as temazepam, zolopidem, and zopiclone, stimulants such as amphetamine and amphetamine-like agents, adrafinil, modafinil, caffeine and chronobiotics substances such as melatonin and, more recently, slow release caffeine. In the sports area, all of these substances except caffeine are on the list of forbidden products, although special authorizations linked to known disease conditions are allowed. In the military setting, the environment may be similar, but the context of use is very different. In the context of a rescue mission, the current practice in the French military organization is to place modafinil pills in the ejection seat of fight planes and in rescue boats. A second context is the use of anti-sleep agents under orders; the debate continues on this and the appropriate recommendations in this context. Self-medication is a third condition, in which case no rules have been defined.

Working on atypical schedules

Shift work has been associated with a number of health problems including cardiovascular disease, impaired glucose and lipid metabolism, gastrointestinal discomfort, reproductive difficulties, and breast cancer. The specific contributions of disturbed physiological rhythms, circadian misalignment, and sleep debt to the various medical problems encountered by shift workers remain to be clarified. Fatigue can be caused by extended on-duty and/or waking periods, inadequate sleep quantity, sleep disturbances, disruption of circadian rhythms, and difficult work and familial conditions. Fatigue-related accidents raise a safety concern for shift workers, especially at the end of the night when the circadian nadir of alertness interacts with increased time awake. Individuals vary greatly in their capacity to adjust to atypical work schedules and their tolerance to circadian misalignment. Predisposing individual and domestic factors have been identified, such as increasing age, being a single woman in charge of children, and split sleep patterns, all of which can affect the ability to adjust to atypical schedules. However, prior studies indicate that predisposing individual and social determinants are generally poor predictors of shift work tolerance in a given individual. In this manuscript, we review several countermeasures to improve adaptation to shift work.

Effects of caffeine on electrophysiological and neuropsychological indices after sleep deprivation

Caffeine is regarded as a central nervous system (CNS) stimulant. The goal of this study was to analyze electrophysiological, motor, cognitive and behavioral changes produced by caffeine ingestion after sleep deprivation. Ten subjects were evaluated after sleep deprivation, comparing the ingestion of either 400 mg of caffeine or placebo, in a double-blind randomized study. The variables analyzed were: quantitative EEG, the event-related potential (ERP-P300) and cognitive responses. The most significant quantitative EEG results, which were characterized by moment x treatment interactions, were seen in alpha and theta relative power variables. A significant decrease in relative alpha and theta was observed in the caffeine group after sleep deprivation. In relation to caffeine stimulant effects, there were no significant differences in the other parameters.

Caffeine and Placebo Expectation

Abstract. Caffeine placebo expectation seems to improve vigilance and cognitive performance. This study investigated the effect of caffeine and placebo expectation on vigilance and cognitive performance during 28 h sleep deprivation. Ten healthy males volunteered to take part in the double-blind, cross-over study, which required participants to complete five treatment periods of 28 h separated by 1-week wash-out intervals. The treatments were no substance (Control); caffeine 200 mg at 00:00 (C200); placebo 200 mg at 00:00 (P200); twice caffeine 200 mg at 00:00 and 04:00 (C200-C200); caffeine 200 mg at 00:00 and placebo 200 mg at 04:00 (C200-P200). Participants were told that all capsules were caffeine and given information about the effects of caffeine to increase expectation. Vigilance was assessed by a three-letter cancellation test, cognitive functions by the continuous addition test and Stroop test, and cardiovascular regulation by heart rate and blood pressure. Tests were performed bihourly from 00:00 to 10:00 of the second day. Results indicated that C200-P200 and C200-C200 were more alert (p < .05) than Control and P200. Their cognitive functions were higher (p < .05) than Control and P200. Also, C200-P200 scored higher than C200 in the letter cancellation task (p < .05). No test showed any significant differences between C200-P200 and C200-C200. The results demonstrated that the combination of caffeine 200 mg and placebo 200 mg expectation exerted prolonged positive effects on vigilance and cognitive performance.

Dolphin continuous auditory vigilance for five days

The present report describes the first study of continuous vigilance in dolphins. Two adult bottlenose dolphins (Tursiops truncatus), WEN (male) and SAY (female), maintained a very high detection rate of randomly presented, infrequent, 1.5-s target tones in a background of frequent 0.5-s equal-amplitude tones over five continuous 120-h sessions. The animals were able to maintain high levels (WEN 97, 87, 99%; SAY 93, 96%) of target detection without signs of sleep deprivation as indicated by behavior, blood indices or marked sleep rebound during 24 h of continuous post-experiment observation. Target response time overall (F = 0.384; P = 0.816) did not change between day 1 and day 5. However, response time was significantly slower (F = 21.566, P = 0.019) during the night (21.00-04.00 h) when the dolphins would have ordinarily been resting or asleep.

Vigilance, alertness, or sustained attention: physiological basis and measurement

Vigilance is a term with varied definitions but the most common usage is sustained attention or tonic alertness. This usage of vigilance implies both the degree of arousal on the sleep-wake axis and the level of cognitive performance. There are many interacting neural and neurotransmitter systems that affect vigilance. Most studies of vigilance have relied on states where the sleep-wake state is altered, e.g. drowsiness, sleep-deprivation, and CNS-active drugs, but there are factors ranging from psychophysics to motivation that may impact vigilance. While EEG is the most commonly studied physiologic measure of vigilance, various measures of eye movement and of autonomic nervous system activity have also been used. This review paper discusses the underlying neural basis of vigilance and its assessment using physiologic tools. Since, assessment of vigilance requires assessment of cognitive function this aspect is also discussed.

Caffeine: implications for alertness in athletes

Caffeine is one of the most widely consumed drugs in the world, taken socially and for its alertness- and performance-promoting actions. Extensive reports assert that caffeine increases alertness and cognitive performance levels and, when taken before exercise, demonstrates ergogenic properties. Caffeine ingestion has been associated with increased performance during endurance submaximal, and acute, high-intensity exercise. The exact mechanism of action for the performance effects of caffeine is unknown, although several physiologically and psychologically based theories exist as to how caffeine achieves increased performance capabilities. This paper outlines the known sites of caffeine activity in the body,and discusses these with respect to the effects of caffeine observed during performance assessments.

Random number generation during sleep deprivation: effects of caffeine on response maintenance and stereotypy

Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. Previous neuropsychological studies indicate that sleep deprivation causes impairments in prefrontal cortical function. Random number generation (RNG) is thought to provide a sensitive index of executive functions that rely on the prefrontal cortex. The present study tested the hypothesis that sleep deprivation would impair RNG and that caffeine would mitigate this impairment. Healthy young men (n = 21) participated in two 40-h sleep deprivations 1 week apart. During each sleep deprivation period subjects received either caffeine or placebo according to a randomized, double-blind cross-over design, and they completed an oral RNG task at 3-h intervals. Comparison of test sessions at analogous times of day revealed that sleep deprivation was associated with significant drops in the number of responses, a threefold increase in the percentage of rule violations, 59% greater response redundancy and a 20% increase in stereotypy of adjacent response pairs. Sleep deprivation did not consistently alter counting tendency. Caffeine ameliorated the decrease in the number of responses but did not mitigate other deficits in RNG that arose during sleep deprivation. These findings are consistent with prior reports of diminished vigilance and increased perseveration during extended wakefulness. They support the conclusion that caffeine preserves simple aspects of cognitive performance during sleep deprivation, whereas caffeine may not prevent detrimental effects of sleep deprivation on some complex cognitive functions.