History of Sleep and Circadian Health

The history of sleep is long and rich. This page provides a brief overview of key developments that have shaped how we now think about sleep and circadian health. By looking back we can see that sleep has had a long rich journey through different eras and cultures, and we can honour the work of our forebears, which has helped us to where we are today.

Sleep has always been important to humans. Some of the earliest documented medical descriptions of sleep date back to ancient Egypt, where sleep medicine was practiced comprehensively even 4000 years ago. They had dedicated sleep temples, described sleep disorders and dream analysis, and even used hypnotics to treat conditions like insomnia. In ancient Greece, Aristotle proposed that a master control organ would shut down to cause sleep. Galen, who came 200 years later proposed that sleep allowed the brain to restore itself, and for digestion to occur, so that the body could recover. Alongside studying physiology, the ancient Greeks saw dreams as having important functions – bringing messages from the gods, and other wisdoms. 

In India, the ancient ayurvedic texts advised that sleep was a basic health requirement that was balanced by diet, mindset and daily routines, and these concepts that are still in use today in modern ayurvedic medicine.

Between the seventh and thirteenth centuries, Arab-Islamic physicians developed detailed ideas about sleep physiology and disorders through more structured research and observations, and even wrote text books on sleep medicine. Al-Rāzī described sleep paralysis; Ibn Sīnā proposed sleep stages based on changes in the pulse, and also described symptoms resembling sleep apnea. Texts also referenced pharmaceutical therapies and herbal remedies for sleep disorders. 

Through medieval Europe sleep was not given as much attention as other biological processes, and in 1662CE sleep was even described as a deficiency in alertness or brain activity by prominent French philosopher, Déscartes. The development of scientific tools such as microscopes helped advance other fields of medicine, but sleep science lagged behind this progress for some time.

The story of circadian science began in 1729, when a French astronomer named Jean-Jacques d’Ortous de Mairan noticed that the leaves of the mimosa plant continued to open and close on a 24-hour rhythm—even in total darkness. This showed that the plant had its own internal clock, or circadian rhythm.  It was an early glimpse of something we now understand more clearly. In humans, we now know that the circadian rhythm is coordinated by a “master clock” in the brain, a tiny structure called the suprachiasmatic nucleus (SCN). This master clock helps our bodies stay in sync with the 24-hour day by aligning everything from sleep to hormone release to body temperature.

Modern sleep science accelerated when electrical brain activity became measurable. In 1929, Hans Berger reported on his use of the human electroencephalogram, or EEG. An EEG is a test that measures the brain’s electrical signals, and in sleep science, EEGs help researchers see how brain activity changes during different stages of sleep.

In 1953, Eugene Aserinsky and Nathaniel Kleitman identified rapid eye movement (REM) sleep, helping overturn the idea that sleep was a single, passive state.

Following on through the 1960s and 1970s the “sleep study” was developed, combining EEG, heart rate measuring, body temperature monitoring and observations. We now call this type of study polysomnography. Today, modern medical instruments have improved our ability to observe and measure what happens during sleep, and have even evolved into personal wearable devices. Much of that progress rests on the shoulders of this prior work. 

Some of the most important advances in circadian science came from discovering the genes that help regulate our internal body clocks.

In the 1980s, researchers identified a gene in fruit flies that helps control their daily rhythms. This discovery opened the door to understanding how biological clocks work at the molecular level.

In 2017, Jeffrey Hall, Michael Rosbash, and Michael Young received the Nobel Prize in Physiology or Medicine for their discoveries about how these clocks operate. Their research showed that certain genes produce proteins whose levels rise and fall in a repeating cycle. This process helps the body keep time, even without constant signals from the outside world.

Another major breakthrough came in the 1980s, when sleep researcher Alexander Borbély proposed the two-process model of sleep regulation. This model explains how two interacting processes influence when we feel sleepy and when we are ready to wake up:

Process C (circadian rhythm): Our internal body clock helps regulate the timing of sleep and wakefulness across the 24-hour day.

Process S (sleep pressure): The longer we stay awake, the stronger our need for sleep becomes. This pressure decreases while we sleep.

Together, these processes help explain why we tend to feel sleepy at certain times of day, why staying awake longer increases our need for sleep, and why our body clock can sometimes keep us alert even when we are tired.

Another important advance in sleep science came from understanding how chemical messengers in the brain help control sleep and wakefulness.

These messengers include neurotransmitters, which carry signals between nerve cells, and neuropeptides, which help regulate how those cells communicate.

In the 1990s, researchers, including Clifford Saper, helped develop the concept of a sleep switch. This model describes how different groups of brain cells work together to keep us awake or help us transition into sleep. Rather than gradually shutting down, the brain can switch between these two states through a balance of signals that promote sleep or wakefulness.

Around the same time, scientists discovered orexin, also called hypocretin, a neuropeptide that helps maintain wakefulness and keeps the sleep-wake system stable. A loss of orexin-producing brain cells is a key feature of narcolepsy type 1, a disorder that causes excessive daytime sleepiness.

These discoveries have improved our understanding of sleep disorders and helped researchers develop medications that target the brain’s sleep-wake system.

Over the past century, sleep science has transformed our understanding of how the brain and body regulate sleep and wakefulness. We now know that sleep is not simply a period of rest. It is an active biological process closely connected to our internal body clock and overall health.

These discoveries have also changed how we approach sleep disorders. Advances in sleep monitoring, genetics, and our understanding of brain chemistry have improved diagnosis and treatment. Researchers continue to explore new therapies and how sleep and circadian rhythms influence health throughout life.

We also understand that circadian rhythms affect much more than sleep. They help regulate our energy levels, metabolism, and mood throughout the day. When these rhythms are disrupted, the effects can extend well beyond a poor night’s sleep.

As research continues, one message becomes increasingly clear: sleep and circadian health are essential parts of overall health. Understanding how our bodies function across the full 24 hours can help us make informed choices and support better health and wellbeing.