Since the early beginning of recorded time, exploratory minds provided us with mounds of discoveries relative to sleep. Many theories and hypotheses have been tested in an attempt to understand sleep, yet only few have been confirmed via scientific research. Several of the scientists listed below suggested that sleep is a reflection of specific brain activity which may be influenced by alterations in the environment. Several of these findings highlight the importance of the HPA-T axis, as the hypothalamus plays a crucial role in circadian rhythm and phasic sleep patterns, two aspects of sleep affected by medication, exposure to light, sugary foods, and activation of neuronal pathways. Brought to you by Harvard Medical School (source), here is a short timeline reflecting the evolution of our understanding of sleep and brain function.
~162 A.D. Galen
Galen, the Greek-born physician, helped lay the foundation for Western medical tradition. He recognized that consciousness resided not in the heart, but in the brain.
~1490 Leonardo da Vinci
Many scholars insisted that Leonardo da Vinci slept only 15 minutes once every two hours, although not officially confirmed. This pattern of sleep, known as “polyphasic sleep”, is sometimes called “daVinci sleep.”
1729 Jean-Jacques d’Ortous deMairan
This French astronomer noticed that heliotrope plants maintain a biological rhythm, opening their leaves in the day and closing them at night. He finds that this rhythm is maintained even when the plant is kept in perpetual darkness. Thus, he is among the first to explore the endogenous nature of circadian rhythms.
1807 Gas Lighting
Although long before this, many cities had created ordinances that required homeowners and business owners to light the fronts of their building with lanterns. Pall Mall, in London becomes the first area in the world to light its streets with gas lights. As this technology is adopted, it not only makes city streets safer, it also enables people to be active and productive long after the sun goes down.
1903 First Sleeping Pill
Barbital, synthesized from barbituric acid by German chemists Emil Fischer and Joseph von Mering, is dispensed in capsules under the trade name “Veronal.” It induces calming drowsiness and sleep with few side effects.
1962 24-Hour Convenience
The convenience store chain 7-Eleven opens its first 24-hour store in Austin, Texas. The chain was originally open from 7am to 11pm. But in response to consumer demand for round-the-clock convenience, 7-Eleven begins opening 24-hour stores around the nation. From this time forward, customers will have access to soda pop and apple pies all hours of the day and night.
1972 Circadian Clock Located
Two pairs of researchers –Robert Moore with Victor Eichler, and F.K. Stephan with Irving Zucker –identify the suprachiasmatic nucleus (SCN), a cluster of approximately 50, 000 neurons located in the hypothalamus, as the body’s internal circadian clock.
1990 SCN Restores Circadian Period
Researchers studying hamsters find that transplanting the SCN can also transfer the donor’s circadian rhythm to the recipient. This experiment provides evidence that the SNC is in fact the master biological clock.
2003 Circadian – Behavioral Neural Pathways
Thomas Chou and colleagues studied the neuronal pathways from the circadian pacemaker, the SCN that influence behaviors. They found that the SCN does not directly send its output to the wake-sleep system, but instead relays its signals through a multi-stage circadian ‘integrator’ (for example, the subparaventricular zone and the dorsomedial nucleus of the hypothalamus). These areas receive other signals, related to the availability of food, external temperature, and stressors such as the presence of predators, which can help shape circadian cycles that allow animals to adapt to their environments.