Elsevier

Brain and Development

Volume 31, Issue 4, April 2009, Pages 255-273
Brain and Development

Review article
A newly proposed disease condition produced by light exposure during night: Asynchronization

https://doi.org/10.1016/j.braindev.2008.07.006Get rights and content

Abstract

The bedtime of preschoolers/pupils/students in Japan has become progressively later with the result sleep duration has become progressively shorter. With these changes, more than half of the preschoolers/pupils/students in Japan recently have complained of daytime sleepiness, while approximately one quarter of junior and senior high school students in Japan reportedly suffer from insomnia. These preschoolers/pupils/students may be suffering from behaviorally induced insufficient sleep syndrome due to inadequate sleep hygiene. If this diagnosis is correct, they should be free from these complaints after obtaining sufficient sleep by avoiding inadequate sleep hygiene. However, such a therapeutic approach often fails. Although social factors are often involved in these sleep disturbances, a novel clinical notion – asynchronization – can further a deeper understanding of the pathophysiology of these disturbances. The essence of asynchronization is a disturbance in various aspects (e.g., cycle, amplitude, phase and interrelationship) of the biological rhythms that normally exhibit circadian oscillation, presumably involving decreased activity of the serotonergic system. The major trigger of asynchronization is hypothesized to be a combination of light exposure during the night and a lack of light exposure in the morning. In addition to basic principles of morning light and an avoidance of nocturnal light exposure, presumable potential therapeutic approaches for asynchronization involve both conventional ones (light therapy, medications (hypnotics, antidepressants, melatonin, vitamin B12), physical activation, chronotherapy) and alternative ones (kampo, pulse therapy, direct contact, control of the autonomic nervous system, respiration (qigong, tanden breathing), chewing, crawling). A morning-type behavioral preference is described in several of the traditional textbooks for good health. The author recommends a morning-type behavioral lifestyle as a way to reduce behavioral/emotional problems, and to lessen the likelihood of falling into 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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