History of Sleep
It is difficult to determine a point in time when an interest in sleep occurred. Likewise, it is nearly impossible to pick a date, person, or event which points to the beginning of sleep research. We could say it was the discovery of opium, a widely offered treatment for insomnia in ancient Egyptian times (~1300 B.C.) and the first hypnotic medication. Or perhaps the history of sleep medicine began much later with Hippocrates’ theory of sleep in Corpus Hippocraticum (~400 B.C.)?
In 350 B.C. Aristotle viewed sleep as “inhibition of sense perception” for “conservation”. In 1729 French Astronomer Jean Jacques d’Ortous deMairan experimented with plants and biological rhythms. He is thought to be the first to experiment with biological rhythms. In 1920 Dr. Nathanial Kleitman explored circadian rhythms and sleep deprivation.
Sleep theories abounded in the 19th century and there were many schools of thought for the cause of sleep. One of the more popular ideas was that sleep was related to the blood vessels, specifically that sleep was due either to congestion or pressure of blood in the brain, or a lack of blood in the brain. Two chemical approaches were also possible concepts for the cause of sleep. The chemical approach implied that sleep was caused by 1) a lack of oxygen to the brain or 2) an accumulation of toxic substances.
A new understanding of the central nervous system, a demonstration of the electrical activity of the nervous system, and the newly named neuron brought on neural theories for the cause of sleep by the mid-19th century. One type of neural theory was that neurons were paralyzed during sleep, preventing communication between other nerve cells.
Based on earlier experiments, behavioral theories were presented in the late 1800s that proposed an “inhibitory reflex” as the cause of sleep. The physiological differences in the states of sleep, dreaming versus quiet sleep were recognized as early as ancient Greece. In 1868, William Griesinger reported eye movements in association with sleep. Before his release of The Interpretation of Dreams in 1900, Freud noted muscle paralysis during sleep that hindered the dreamer from acting out their dreams.
By the mid-1900s, the combined efforts of many researchers concluded that sleep was the loss of wakefulness stimuli from the ascending reticular activating system in the brainstem, the system of nerve pathways in the brain that are concerned with levels of consciousness.
This is the most interesting definition. Sleep is a level of consciousness just as wake is a level of consciousness. Of course there are many levels of consciousness within wake as there are within sleep.
In 1996, the American Medical Association recognized sleep medicine as a specialty. That date belies the importance and interest in sleep that has been going on essentially since the beginning of time.