Overview

Neuroscience research can be of great help in improving school performance in children and adolescents. We know, for instance, that sleep deprivation significantly impairs memory and the acquisition of many skills, and disturbs emotional and cognitive performance as well. By inducing sleep deprivation in many people in most urban environments, modern 24-hour society can become a threat to healthy behavior. Adolescents, in particular, tend to sleep less during school time because of late bedtime (work or entertainment) and early schooling. This current cultural pattern is out of phase with the body's internal clock and the circadian rhythms that are the result of millions of years of biological adaptation in mammals. People certainly are not prepared to be awake when our body temperature is at a minimum, for instance. Moreover the cyclical pattern of sleeping and waking changes with age. Adolescents show a shift toward a more owl-like behavior and their optimal time of the day is generally in the evening. This is the reason why they can be sleepy in the morning and become more alert when their classes are mostly over. By paying attention to these facts of chronoeducation, schools can improve student learning by creating a better connection between diurnal rhythms and the school schedule.

The Editors

Many biological functions wax and wane in cycles that repeat each day, month, or year. Such patterns do not reflect simply organism's passive response to environmental changes.

Biosynthesis and metabolism of melatonin

Melatonin was isolated in 1958 by Lerner and his associates, its chemical nature being identified as N-acetyl-5-methoxytryptamine (Lerner et al. 1958, 1959) (Fig. 10.1). In vertebrates, melatonin is primarily secreted by the pineal gland. Synthesis also occurs in other cells and organs including the retina (Cardinali and Rosner 1971; Tosini and Menaker 1998; Liu et al. 2004), human and murine bone marrow cells (Conti et al. 2000), platelets (Champier et al. 1997), gastrointestinal tract (Bubenik 2002), skin (Slominski et al. 2005a,b), or lymphocytes (Carrillo-Vico et al. 2004). However, circulating melatonin is derived only from the pineal gland, as shown by its disappearance after pineal removal. Since there is no storage of melatonin in the pineal gland, and since the circulating melatonin is degraded rapidly by the liver, plasma levels of melatonin reflect pineal biosynthetic activity.

Melatonin secretion is synchronized to the light/dark (LD) cycle, with a nocturnal maximum (in young humans, about 200 pg/ml plasma) and low diurnal baseline levels (about 10 pg/ml plasma). Studies have supported the value of the exogenous administration of melatonin in circadian rhythm sleep disorders, insomnia, cancer, neurodegenerative diseases, disorders of the immune function, and oxidative damage (Karasek et al. 2002; Pandi-Perumal et al. 2005, 2006; Srinivasan et al. 2005a,b, 2006; Hardeland et al. 2006).