A wise man was once asked, “What is the most precious thing?” As he was very wise, instead of answering in terms of precious metals his answer was, “Sleep is the most precious thing of all, for which a person would fight with any and all!”
Though we spend almost one third of our life in sleep, it is the most poorly understood phenomenon in the human body. This is not to say that the subject of sleep has been ignored. Far from it! Our oldest books and stories are replete with references to dreams and with theories on the origin and need for sleep. This has been addressed in both religious and secular literature. Important historical events were foreshadowed by dreams e.g. Constantine, the future Roman emperor, dreamed before the battle of the Milvian Bridge that if he would convert to Christianity, he would win. Before this battle most of Europe was non-Christian. Constantine converted, won the battle and later spread the Christian religion over all his empire sowing the seeds for the rise of the Christian Church.
Hippocrates thought that sleep was due to the cooling of the blood during night, while Aristotle thought the heat generated by food induced sleep! And so it continued for many centuries, with no clear answer on the question. Modern scientific investigation of sleep began in the early twentieth century, with the development of electroencephalography i.e. the study of brain waves. The analysis of brain wave data accumulated by studies during wakefulness and sleep led to the discovery that the brain did not shut off completely during sleep. Rather, it kept working, albeit at a different level.
Scientific study has revealed that sleep can be divided into two main stages – non rapid eye movement (NREM) and rapid eye movement (REM). These stages cycle continuously throughout the night. NREM sleep includes the stage of sleep immediately after the onset of sleep and also deep sleep, while REM sleep is the stage of sleep associated with dreams. Both these components of sleep are essential for proper and restful sleep.
Sleep is not a static phenomenon – the duration and timing of sleep is affected by many diverse factors like age, gender, social norms, etc. Sleep is controlled in the body by an area in the brain referred to as the sleep centre, which functions as a switch to on and off sleep. The master control for this switch is light – natural or artificial. Exposure to natural sunlight sets up an internal biological clock, called the circadian rhythm, responsible for our daily wake and sleep times. Exposure to artificial light has led to a change in the circadian rhythm with late night awakening and disturbances in the sleep-wake cycle. Communities which are predominantly rural and not exposed to modern societal influences have more conventional ‘early to bed, early to rise’ sleep wake cycles.
In summary, sleep, though a poorly understood phenomenon throughout history, is now being explored on a much more scientific basis. Understanding the natural cycles of sleep can help one in adjusting better to the vagaries and pressures of modern city life.
