Review articleA newly proposed disease condition produced by light exposure during night: Asynchronization
Introduction
The suprachismatic nucleus (SCN) is the site where circadian rhythms are generated. The SCN develops throughout the course of gestation, but is still immature for some time after birth. The SCN is suggested to be vulnerable to maternal influences [1]. Since disturbances of circadian rhythms in the young can impact the function of the SCN in the subsequent lifespan, techniques to deal with them are much needed. However, we have little knowledge about the pathophysiology of the disruption of circadian rhythms in the clinical setting, making it difficult to find an appropriate clinical approach to treat these patients. It is very difficult at present to take adequate measures against circadian disruptions in patients.
This review article introduces the recent phenomenon of a nocturnal lifestyle among preschoolers/pupils/students in Japan, and the association between this nocturnal lifestyle and behavior. Then, the presumed involvement of the biological clock and the serotonergic system in those who prefer a nocturnal lifestyle are reviewed. Finally, a new clinical entity – asynchronization – is proposed, in an attempt to elucidate the pathophysiology of circadian disruptions from which many preschoolers/pupils/students in Japan are evidently suffering, and to provide new clinical therapeutic approaches.
Section snippets
Recent figures on bedtime and sleep duration of preschoolers/pupils/students in Japan
The percentage of 1-year-old children who went to bed later than 22:00 in Japan was 25.7%, 35.4%, 40.2%, and 54.4% in 1980, 1990, 1995, and 2000, respectively [2]. For 3-year-old children, these respective figures were 21.7%, 35.5%, 37.2%, and 52.0%. Kohyama et al. found that the latter figures were 43.8% in 1999 [3], and 49.8% in 1999–2000 [4]. In addition, in 2004, 51.1% of the 3-year-old children in Fukuoka went to bed later than 22:00 [5].
In 1979, no fourth grade pupils of the elementary
Nocturnal lifestyles and behaviors
A shortage of sleep, and delayed bedtimes and wake-up times are known to produce physical, mental, and/or emotional problems.
Presumed involvement of the biological clock and serotonergic system on unhealthy conditions seen in late risers and sleepers
Taking these reports on preschoolers together with previously cited papers on older children, adolescents, and adults, problematic behaviors are likely to be associated with delayed wake-up times, delayed bedtimes, and an irregular lifestyle. Although delayed bedtimes also produced sleep loss [4], problematic behaviors are found to be likely to be associated with delayed wake-up times, delayed bedtimes, and an irregular lifestyle, regardless of sleep duration [44]. In the following section, the
Asynchronization
More than half of the preschoolers/pupils/students in Japan complain about daytime sleepiness, while about one quarter of junior high school students in Japan suffer from insomnia. Indeed, more than 20% of the pupils/students in Japan complained of “a need to yawn”, “desire to lie down”, “irritation”, “hypersensitivity”, “neck stiffness”, and “lumbago”. Since these complaints were compatible with the associated features of behaviorally induced insufficient sleep syndrome [25], these
Conclusions
Many children in Japan, from youngsters to senior high school students, suffer from both daytime sleepiness and nocturnal insomnia, and are persistently tired and inactive. Are these complaints explained only by sleep insufficiency? This article focused on the association between nocturnal lifestyle and the problems of these preschoolers/pupils/students with special reference to the biological clock and the serotonergic system, although involvements of dopamine [170], opioid peptide [89] and so
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