Patricia Sagaspe

The circadian and homeostatic modulation of sleep pressure during wakefulness differs between morning and evening chronotypes

The purpose of this study was to evaluate homeostatic and circadian sleep process in ‘larks’ and ‘owls’ under daily life conditions. Core body temperature, subjective sleepiness and waking electroencephalogram (EEG) theta–alpha activity (6.25–9 Hz) were assessed in 18 healthy men (nine morning and nine evening chronotypes, 21.4 ± 1.9 years) during a 36‐h constant routine that followed a week of a normal ‘working’ sleep–wake schedule (bedtime: 23.30 h, wake time: 07.30 h). The phase of the circadian rhythm of temperature and sleepiness occurred respectively, 1.5 h (P = 0.01) and 2 h (P = 0.009) later in evening‐ than in morning‐type subjects. Only morning‐type subjects showed a bimodal rhythm of sleep–wake propensity. The buildup of subjective sleepiness, as quantified by linear regression, was slower in evening than in morning types (P = 0.04). The time course of EEG theta–alpha activity of both chronotypes could be closely fitted by an exponential curve. The time constant of evening types was longer than that of morning types (P = 0.03), indicating a slower increase in sleep pressure during extended wakefulness. These results suggest that both the circadian signal and the kinetics of sleep pressure buildup differ between the two chronotypes even under prior naturalistic conditions mimicking the usual working day.

Effects of sleep deprivation on Color-Word, Emotional, and Specific Stroop interference and on self-reported anxiety

The aim of this study was principally to assess the impact of sleep deprivation on interference performance in short Stroop tasks (Color-Word, Emotional, and Specific) and on subjective anxiety. Subjective sleepiness and performance on a psychomotor sustained attention task were also investigated to validate our protocol of sleep deprivation. Twelve healthy young subjects were tested at four-hourly intervals through a 36-h period of wakefulness under a constant routine protocol. Analyses of variance for repeated measurements revealed that self-assessment of sleepiness on a visual analogue scale as well as mean reaction time performance on the sustained attention task, both for the first minute and for 10 min of testing, were worsened by sleep deprivation. Analyses revealed an increase in self-reported anxiety scores on the STAI questionnaire but did not reveal any significant effect after sleep deprivation either on indexes of interference or on accuracy in Stroop tasks. However, analyses showed sensitivity to circadian effect on verbal reaction times in the threat-related (Emotional) and sleep-related (Specific) Stroop tasks. We concluded that 36 h of prolonged wakefulness affect self-reported anxiety and Emotional Stroop task resulting in a cognitive slowing. Moreover, total sleep deprivation does not affect interference control in any of the three short Stroop tasks.

Age, performance and sleep deprivation

Young subjects are frequently involved in sleep‐related accidents. They could be more affected than older drivers by sleep loss and therefore worsen their driving skills quicker, or have a different perception of their level of impairment. To test these hypotheses we studied variations of reaction time (RT), a fundamental prerequisite for safe performing, as measured by lapses, i.e. responses ≥500 ms and self‐assessment of performance and sleepiness after a night awake and after a night asleep in a balanced crossover design in young versus older healthy subjects. Ten young (20–25 years old) and 10 older volunteers (52–63 years old) were tested with and without 24 h of sleep deprivation. Without sleep deprivation, RTs were slower in older subjects than in the younger ones. However, after sleep deprivation, the RTs of young subjects increased while that of the older subjects remained almost unaffected. Sleepiness and self‐perception of performance were equally affected in both age groups showing different perception of performance in the age groups. Our findings are discussed in terms of vulnerability to sleep‐related accidents.

Sleep disorders and accidental risk in a large group of regular registered highway drivers

OBJECTIVE Despite convincing evidence regarding the risk of highway accidents due to sleepiness at the wheel, highway drivers still drive while sleepy. Sleep disorders can affect driving skills, but the relative impact of sleep complaints among a large population of highway drivers is still unknown. METHODS Out of 37,648 questionnaires completed by frequent highway users (registered in an electronic payment system), we ran our analyses on 35,004 drivers who responded to all items. The questionnaire previously used in a telephone survey included socio-demographics, driving and sleep disorders items (Basic Nordic Sleep Questionnaire) and the Epworth Sleepiness Scale. RESULTS Of all drivers, 16.9% complained of at least one sleep disorder, 5.2% reported obstructive sleep apnea syndrome, 9.3% insomnia, and 0.1% narcolepsy and hypersomnia; 8.9% of drivers reported experiencing at least once each month an episode of sleepiness at the wheel so severe they had to stop driving. One-third of the drivers (31.1%) reported near-miss accidents (50% being sleep-related), 2520 drivers (7.2%) reported a driving accident in the past year, and 146 (5.8%) of these driving accidents were sleep-related. The highest risk of accidents concerned patients suffering from narcolepsy and hypersomnia (odds ratio 3.16, p<.01) or multiple sleep disorders (odds ratio 1.46, p<.001). Other major risk factors were age [18-30 years (OR 1.42, p<.001)] and being unmarried (OR 1.21-fold, p<.01). CONCLUSIONS In regular highway drivers, sleepiness at the wheel or sleep disorders such as hypersomnia and narcolepsy are responsible for traffic accidents independent of age, sex, marital status or socio-professional categories.

Fear and stop: a role for the amygdala in motor inhibition by emotional signals.

Rapid interruption of ongoing motor actions is crucial to respond to unexpected and potentially threatening situations. Yet, it remains unclear how motor inhibition interacts with emotional processes. Here we used a modified stop-signal task including an emotional component (fearful faces) to investigate whether neural circuits engaged by action suppression are modulated by task-irrelevant threat-related signals. Behavioral performance showed that reaction times were prolonged in the presence of incidental threat information, and this emotional slowing was enhanced when incorrect responses were made following stop signals. However, the speed and efficacy of voluntary inhibition was unaffected by emotion. Brain imaging data revealed that emotional cues during stop trials interacted with activity in limbic regions encompassing the basal amygdala and sublenticular extended amygdala region, as well as with the supplementary motor area (SMA). In addition, successful motor inhibition to threat signals selectively recruited a region in lateral orbitofrontal cortex, distinct from areas in inferior frontal gyrus typically associated with voluntary inhibition. Activity in primary motor cortex was lower when incorrect responses were made on stop signal trials accompanied by a fearful face, relative to neutral, in parallel with the slower response times observed behaviorally. Taken together, our findings suggest that the amygdala may not only promote protective motor reactions in emotionally-significant contexts (such as freezing or defensive behavior) but also influence the execution of ongoing actions by modulating brain circuits involved in motor control, so as to afford quick and adaptive changes in current behavior.

Maintenance of Wakefulness test, obstructive sleep apnea syndrome, and driving risk

Sleepiness at the wheel is a major risk factor for traffic accidents. Because of the potential medical and legal implications, in this study, we evaluated the correlation between subjective and objective measures of sleepiness and driving performances in patients suffering from excessive daytime sleepiness.

Extended Driving Impairs Nocturnal Driving Performances

Though fatigue and sleepiness at the wheel are well-known risk factors for traffic accidents, many drivers combine extended driving and sleep deprivation. Fatigue-related accidents occur mainly at night but there is no experimental data available to determine if the duration of prior driving affects driving performance at night. Participants drove in 3 nocturnal driving sessions (3–5am, 1–5am and 9pm–5am) on open highway. Fourteen young healthy men (mean age [±SD] = 23.4 [±1.7] years) participated Inappropriate line crossings (ILC) in the last hour of driving of each session, sleep variables, self-perceived fatigue and sleepiness were measured. Compared to the short (3–5am) driving session, the incidence rate ratio of inappropriate line crossings increased by 2.6 (95% CI, 1.1 to 6.0; P<.05) for the intermediate (1–5am) driving session and by 4.0 (CI, 1.7 to 9.4; P<.001) for the long (9pm–5am) driving session. Compared to the reference session (9–10pm), the incidence rate ratio of inappropriate line crossings were 6.0 (95% CI, 2.3 to 15.5; P<.001), 15.4 (CI, 4.6 to 51.5; P<.001) and 24.3 (CI, 7.4 to 79.5; P<.001), respectively, for the three different durations of driving. Self-rated fatigue and sleepiness scores were both positively correlated to driving impairment in the intermediate and long duration sessions (P<.05) and increased significantly during the nocturnal driving sessions compared to the reference session (P<.01). At night, extended driving impairs driving performances and therefore should be limited.

Sleepiness, near-misses and driving accidents among a representative population of French drivers

Study objectives were to determine the prevalence of sleepy driving accidents and to explore the factors associated with near‐miss driving accidents and actual driving accidents in France. An epidemiological survey based on telephone interviews was conducted on a representative sample of French drivers. The questionnaire included sociodemographics, driving and sleep disorder items, and the Epworth sleepiness scale. Of 4774 drivers (response rate: 86%), 28% experienced at least one episode of severe sleepiness at the wheel (i.e. requiring to stop driving) in the previous year; 11% of drivers reported at least one near‐miss accident in the previous year (46% sleep‐related); 5.8% of drivers reported at least one accident, 5.2% of these being sleep related (an estimate of 90 000 sleep‐related accidents per year in France). Sleepy driving accidents occurred more often in the city (53.8%), during short trips (84.6%) and during the day (84.6%). Using logistic regression, the best predictive factor for near‐misses was the occurrence of at least one episode of severe sleepiness at the wheel in the past year [odds ratio (OR) 6.50, 95% confidence interval (CI), 5.20–8.12, P < 0.001]. The best predictive factors for accidents were being young (18–30 years; OR 2.13, 95% CI, 1.51–3.00, P < 0.001) and experiencing at least one episode of severe sleepiness at the wheel (OR 2.03, 95% CI, 1.57–2.64, P < 0.001). Sleepiness at the wheel is a risk factor as important as age for traffic accidents. Near‐misses are highly correlated to sleepiness at the wheel and should be considered as strong warning signals for future accidents.

Effect of fatigue on performance measured by a driving simulator in automobile drivers

OBJECTIVE To identify risk factors of performance decrement in automobile drivers. METHODS 114 drivers (age <30 years, n=57; age > or =30 years, n=57) who stopped at a rest stop area on a freeway were recruited for the study. They filled out a questionnaire on their journey, sleep/wake patterns and performed a 30-min test on a driving simulator. The test evaluates, by computerized analysis, the lateral deviation of a virtual car from an appropriate trajectory on a virtual road. A sex/age matched control group was recruited in the community. Control subjects were studied at the same time of day as the index case driver. Controls had normal sleep wake schedule, absence of long driving and performed the same driving test. RESULTS Drivers performed significantly worse than controls on the driving test. Age and duration of driving were the main factors associated with decreased performance. CONCLUSION Our driving simulator can identify fatigue generated by driving but results must be considered in relation with age of subjects.

Prolonged nocturnal driving can be as dangerous as severe alcohol-impaired driving

In industrialized countries one‐fifth of all traffic accidents can be ascribed to sleepiness behind the wheel. Driver sleepiness can have many causes, including the use of medicinal drugs or prolonged driving. The present study compared the effects of prolonged highway driving at night with driving impairment caused by alcohol. A cross‐over balanced design tested 14 healthy young men who drove three sessions during night‐time on the open road. The driving sessions were of 2, 4 and 8 h (03:00–05:00, 01:00–05:00 and 21:00–05:00 hours) duration. Standard deviation of lateral position (SDLP, cm), measuring the weaving of the car in the last driving hour of each session, was the primary parameter. Only 2 h of continuous nocturnal driving were sufficient to produce driving impairment comparable to a blood alcohol concentration (BAC) of 0.05%; after 3 h of driving impairment corresponds to a BAC of 0.08%. In conclusion, a maximum of two continuous nocturnal driving hours should be recommended.