What Is sleepiness? Association between Subjective and Objective Sleepiness with Cognitive Function

Y. Komada Meiji Pharmaceutical University, Tokyo, Japan

Keywords: sleepiness; sleep disorder; performance; traffic accident.

Introduction. Sleep is an important aspect of one’s daily life, and about one-third of a person’s life is spent sleeping. However, the proportion of people getting less than the recommended hours of sleep is increasing. Insufficient sleep is associated with modern lifestyle factors, such as psychological stress, electronic media use, sedentary behavior, and poor diet, and leads to sleepiness, cognitive dysfunction, and has adverse effects on performance at school and work.

Various methods have been developed to assess daytime sleepiness. The Multiple Sleep Latency Test (MSLT) is a gold standard for objectively quantifying sleepiness. The Psychomotor Vigilance Task (PVT) is an objective measurement that examines accuracy and speed of the task. The Epworth Sleepiness Scale (ESS) subjectively assesses sleepiness. It is also important to diagnose excessive sleepiness because it is associated with morbidity and increased mortality.

Insufficient sleep and daytime sleepiness. A total of 1243 patients, who visited an outpatient clinic in Tokyo, Japan, over one year and presented excessive daytime sleepiness as the chief complaint, were retrospectively investigated. Diagnoses based on the International Classification of Sleep Disorders identified based on the results of a polysomnography, MSLT, ESS, and medical interview were sleep apnea (34.7%), hypersomnia (10.9%), narcolepsy (8.8%), insufficient sleep syndrome (7.1%), and circadian rhythm sleep disorder (6.1%). Insufficient sleep syndrome was the fourth most prevalent diagnosis among patients with excessive daytime sleepiness.

Participants’ scores on the ESS indicated that insufficient sleep syndrome scored lower than that for narcolepsy and hypersomnia but higher than that for sleep apnea and circadian rhythm sleep disorder. About 22% of patients with insufficient sleep syndrome reported having accidents or near-miss accidents in the past 5 years, and this group showed higher ESS scores than the group that did not report any accidents.

The results indicate that a large number of patients were unaware that their sleep duration was insufficient and that people with severe cases of sleep disorder are at high risk of accidents [1].

Sleepiness and accidents. Findings of a well-controlled laboratory experiment suggest that chronic restriction of sleep to 6 h or less per night can seriously impair neurobehavioral functions (as measured by the PVT), while subjects were largely unaware of their sleepiness (as measured by the ESS) and increasing cognitive deficits [2]. We investigated the rate of motor vehicle accidents in the preceding 5 years among Japanese male drivers with sleep apnea syndrome (n = 616, average age: 46.3 (SD: 10.1) years) and age-matched male controls (n = 600). The odds ratio of accidents in the patients group compared to the control group was 2.36. A multivariate logistic regression analysis revealed that accidents were significantly associated with either subjective sleepiness beyond normal limits (ESS ≥ 11) or with serious respiratory disorders (apnea hypopnea index: AHI ≥ 40). AHI scores were significantly higher in the group with two or more accidents in the past 5 years than in the group with only one accident, despite the ESS score in the former group being significantly lower. The results suggest that self-reported measures tend to underestimate the severity of sleepiness [3].

Sleepiness among children and adolescents. The ESS is considered a sensitive measure of daytime sleepiness; however, because the aspects measured in the ESS concern adults (e. g. driving, attending a meeting), the scale is not applicable to younger age groups. Thus, the Pediatric Daytime Sleepiness Scale (PDSS) was developed based on the ESS, which was applicable to school-aged children and adolescents. The PDSS was translated into several languages, including Russian [4] and Japanese [5]. We conducted a survey using the Japanese version of PDSS with 493 students aged 11–16 years (46.2% boys). Results showed that age was significantly correlated with the PDSS-J score (Pearson’s r = 0.53, p = 0.001). A multivariate logistic regression analysis revealed that both sleep duration on school days (OR = 0.74, 95% CI: 0.61–0.90, p = 0.002) and social jetlag, which is misalignment between mid-sleep on weekday and mid-sleep on weekends, (OR = 1.31, 95% CI: 1.04–1.67, p = 0.002) were significantly associated with daytime sleepiness (PDSS score ≥ 15), after adjusting for age and sex. Interestingly, PDSS-J scores were significantly higher in the group with greater social jetlag with or without sufficient sleep duration than in the group with sufficient sleep duration and less social jetlag.

Conclusion. Insufficient sleep syndrome and sleep apnea syndrome seriously impair waking neurobehavioral function and cause traffic accidents in healthy adults. Results suggested that participants were largely unaware of increasing cognitive deficits, which may explain why the impact of chronic sleep impairment on cognitive functions is often assumed to be benign.


  1. Komada Y. et al. Clinical significance and correlates of behaviorally induced insufficient sleep syndrome // Sleep Med. 2008. № 9 (8). P. 851–856.
  2. Van Donge HPA et al. The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation // Sleep. 2003. № 26 (2). P. 117–126.
  3. Komada Y. et al. Elevated risk of motor vehicle accident for male drivers with obstructive sleep apnea syndrome in the Tokyo metropolitan area // Tohoku J. Exp. Med. 2009. № 219 (1). P. 11–16.
  4. Randler C. et al. Psychometric properties of the Russian version of the Pediatric Daytime Sleepiness Scale (PDSS) // Heliyon. 2019. № 5 (7). P. e02134. 5. Komada Y. et al. Social jetlag affects subjective daytime sleepiness in school-aged children and adolescents: A study using the Japanese version of the Pediatric Daytime Sleepiness Scale (PDSS-J) // Chronobiol Int. 2016. № 33 (10). P. 1311–1319.

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28 янв 2020

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    Komada Y. What Is sleepiness? Association between Subjective and Objective Sleepiness with Cognitive Function // Cognitive Neuroscience — 2019: материалы международного форума. Екатеринбург, 6–7 ноября 2019 г. / отв. ред. А.А. Печеркина, С.В. Попов. – Екатеринбург: Урал. ун‑та, 2020. – С. 96-98.

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