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Circadian rhythm disorders among adolescents: assessment and treatment options

Lethargics are to be laid in the light, and exposed to the rays of the sun for the disease is gloom.

Aretaeus of Cappadocia, celebrated Greek physician, 1st century CE

Circadian rhythm and the biological clock

Biologically, the timing and duration of sleep are regulated by two interacting systems — the homoeostatic sleep drive (process S) and the circadian system (process C).1 Process S assumes that the longer one stays awake, the more pressure there is to fall asleep. Once asleep, this pressure dissipates until a homoeostatic equilibrium is achieved. Process C regulates the timing of sleep by controlling periods of biological activity and inactivity throughout the day. These peaks and troughs in biological functioning are known as circadian rhythms and run for slightly longer than 24 hours in humans.2 Circadian rhythms are generated by the central nervous system pacemaker, the hypothalamic suprachiasmatic nucleus (SCN), sometimes called the body clock. The SCN regulates the rhythmicity of many biological processes, such as temperature and hormone release, and is…