Before the invention of electric lighting, humans were primarily exposed to intense (>300 lux) or dim (<30 lux) environmental light—stimuli at extreme ends of the circadian system’s dose–response curve to light. Today, humans spend hours per day exposed to intermediate light intensities (30–300 lux), particularly in the evening. Interindividual differences in sensitivity to evening light in this intensity range could therefore represent a source of vulnerability to circadian disruption by modern lighting. We characterized individual-level dose–response curves to light-induced melatonin suppression using a within-subjects protocol. Fifty-five participants (aged 18–30) were exposed to a dim control (<1 lux) and a range of experimental light levels (10–2,000 lux for 5 h) in the evening. Melatonin suppression was determined for each light level, and the effective dose for 50% suppression (ED50) was computed at individual and group levels. The group-level fitted ED50 was 24.60 lux, indicating that the circadian system is highly sensitive to evening light at typical indoor levels. Light intensities of 10, 30, and 50 lux resulted in later apparent melatonin onsets by 22, 77, and 109 min, respectively. Individual-level ED50 values ranged by over an order of magnitude (6 lux in the most sensitive individual, 350 lux in the least sensitive individual), with a 26% coefficient of variation. These findings demonstrate that the same evening-light environment is registered by the circadian system very differently between individuals. This interindividual variability may be an important factor for determining the circadian clock’s role in human health and disease.

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Night-shift workers are at high risk of drowsiness-related motor vehicle crashes as a result of circadian disruption and sleep restriction. However, the impact of actual night-shift work on measures of drowsiness and driving performance while operating a real motor vehicle remains unknown. Sixteen night-shift workers completed two 2-h daytime driving sessions on a closed driving track at the Liberty Mutual Research Institute for Safety: (i) a postsleep baseline driving session after an average of 7.6 ± 2.4 h sleep the previous night with no night-shift work, and (ii) a postnightshift driving session following night-shift work. Physiological measures of drowsiness were collected, including infrared reflectance oculography, electroencephalography, and electrooculography. Driving performance measures included lane excursions, near-crash events, and drives terminated because of failure to maintain control of the vehicle. Eleven near-crashes occurred in 6 of 16 postnight-shift drives (37.5%), and 7 of 16 postnight-shift drives (43.8%) were terminated early for safety reasons, compared with zero near-crashes or early drive terminations during 16 postsleep drives (Fishers exact: P = 0.0088 and P = 0.0034, respectively). Participants had a significantly higher rate of lane excursions, average Johns Drowsiness Scale, blink duration, and number of slow eye movements during postnight-shift drives compared with postsleep drives (3.09/min vs. 1.49/min; 1.71 vs. 0.97; 125 ms vs. 100 ms; 35.8 vs. 19.1; respectively, P < 0.05 for all). Night-shift work increases driver drowsiness, degrading driving performance and increasing the risk of near-crash drive events. With more than 9.5 million Americans working overnight or rotating shifts and one-third of United States commutes exceeding 30 min, these results have implications for traffic and occupational safety. drowsy driving | sleep | EEG | infrared oculography | fatigue

SUMMARYTo assess the relationships between sleepiness and the incidence of adverse driving events in nurses commuting to and from night and rotating shifts, 27 rotating and permanent night shift-working nurses were asked to complete daily sleep and duty logs, and wear wrist-activity monitors for 2 weeks (369 driving sessions). During all commutes, ocular measures of drowsiness, including the Johns Drowsiness Scale score, were assessed using the Optalertä system. Participants self-reported their subjective sleepiness at the beginning and end of each drive, and any events that occurred during the drive. Rotating shift nurses reported higher levels of sleepiness compared with permanent night shift nurses. In both shift-working groups, self-reported sleepiness, drowsiness and drive events were significantly higher during commutes following night shifts compared with commutes before night shifts. Strong associations were found between objective drowsiness and increased odds of driving events during commutes following night shifts. Maximum total blink duration (mean = 7.96 s) during the drive and pre-drive Karolinska Sleepiness Scale (mean = 5.0) were associated with greater incidence of sleep-related events [OR, 5.35 (95% CI, 1.32, 21.60), OR, 1.69 (95% CI, 1.04, 2.73), respectively]. Inattention was strongly associated with a Johns Drowsiness Scale score equal to or above 4.5 [OR, 4.58 (95% CI,]. Hazardous driving events were more likely to occur when drivers had been awake for 16 h or more [OR, 4.50 (95% CI, 1.81, 11.16)]. Under real-world driving conditions, shift-working nurses experience high levels of drowsiness as indicated by ocular measures, which are associated with impaired driving performance following night shift work.

SUMMARYAlthough it is well known that sleep loss results in poor judgement and decisions, little is known about the influence of social context in these processes. Sixteen healthy young adults underwent three games involving bargaining (ÔUltimatumÕ and ÔDictatorÕ) and trust, following total sleep deprivation (TSD) and during rested wakefulness (RW), in a repeated-measures, counterbalanced design. To control for repeatability, a second group (n = 16) was tested twice under RW conditions. Paired anonymously with another individual, participants made their simple social interaction decisions facing real monetary incentives. For bargaining, following TSD participants were more likely to reject unequal-split offers made by their partner, despite the rejection resulting in a zero monetary payoff for both participants. For the trust game, participants were less likely to place full trust in their anonymous partner. Overall, we provide novel evidence that following TSD, the conflict between personal financial gain and payoff equality is focused upon avoidance of unfavourable inequality (i.e. unfairness). This results in the rejection of unfair offers at personal monetary cost, and the lack of full trust which would expose one to being exploited in the interaction. As such, we suggest that within a social domain decisions may be more influenced by emotion following TSD, which has fundamental consequences for real-world decision-making involving social exchange.k e y w o r d s bargaining, interaction, sleep loss, social preference, trust

Shortened sleep and circadian misalignment, as seen in shift workers, has adverse metabolic and behavioral consequences which lead to obesity and associated comorbidities. This study demonstrates a simulated night shift enhances preference for high fat foods, which may be a contributing factor for shift work-related weight gain. Increasing awareness of changes in food preference may promote healthier food choices. Key terms: diet; dietary intake; eating; fat; food; habit; health; health; high-fat food; night duty; night shift; night work; nutrition; obesity; shift work; shift worker; simulated night shift; sleep loss; weight gain This article in PubMed: www.ncbi.nlm.nih.gov/pubmed/25699635 288 Scand J Work Environ Health 2015, vol 41, no 3Short communication Scand J Work Environ Health. 2015;41(3):288-293. doi:10.5271/sjweh.3486 Enhanced preference for high-fat foods following a simulated night shift by Sean W Cain, PhD,1 Ashleigh J Filtness, PhD,2 Craig L Phillips, PhD,3,4 Clare Anderson, PhD 1,5 Cain SW, Filtness AJ, Phillips CL, Anderson C. Enhanced preference for high-fat foods following a simulated night shift. Scand J Work Environ Health. 2015;41(3):288-293. doi:10.5271/sjweh.3486 Objectives Shift workers are prone to obesity and associated co-morbidities such as diabetes and cardiovascular disease. Sleep restriction associated with shift work results in dramatic endocrine and metabolic effects that predispose shift workers to these adverse health consequences. While sleep restriction has been associated with increased caloric intake, food preference may also play a key role in weight gain associated with shift work. This study examined the impact of an overnight simulated night shift on food preference.Methods Sixteen participants [mean 20.1, standard deviation (SD) 1.4 years; 8 women] underwent a simulated night shift and control condition in a counterbalanced order. On the following morning, participants were provided an opportunity for breakfast that included high-and low-fat food options (mean 64.8% and 6.4% fat, respectively). ResultsParticipants ate significantly more high-fat breakfast items after the simulated night shift than after the control condition [167.3, standard error of the mean (SEM) 28.7) g versus 211.4 (SEM 35.6) g; P=0.012]. The preference for high-fat food was apparent among the majority of individuals following the simulated night shift (81%), but not for the control condition (43%). Shift work and control conditions did not differ, however, in the total amount of food or calories consumed.Conclusions A simulated night shift leads to preference for high-fat food during a subsequent breakfast opportunity. These results suggest that food choice may contribute to weight-related chronic health problems commonly seen among night shift workers.Key terms diet; dietary intake; eating; food; habit; health; night duty; night work; nutrition; obesity; shift work; shift worker; sleep loss; weight gain. Working shifts outside of regular working hours is prevalent in modern industrialize...

Low frequency (< 1 Hz) delta EEG in sleep is of increasing interest as it indicates cortical reorganization, especially in the prefrontal cortex (PFC). Other research shows that delta power in sleep is positively linked to waking cerebral metabolic rate. Such findings suggest that < 1 Hz activity may reflect waking performance at neuropsychological tests specific to the PFC. We investigated this unexplored area. Sleep EEGs (Fp1-F3, Fp2-F4, O1-P3, O2-P4) were recorded in 24 healthy 61-75-year-olds. We found significant associations between 0.5-1.0 Hz power from the left frontal EEG channel, in the first non-REM period, and performance at tasks more specific to the left PFC (e.g., nonverbal planning and verbal fluency). This association was absent from the posterior channels. Neither age nor response times were confounding factors. This potential sleep EEG marker for PFC neuropsychological function in healthy, older people also points to further uses of the sleep EEG in understanding the role of sleep.

Chronic sleep deficiency caused progressive degradation in residents' neurobehavioral performance and exacerbated the effects of acute sleep loss inherent in the 24- to 30-h EDWS that are commonly used in resident schedules.