For thousands of years, sleep remained a little understood but fascinating part of human existence – so mysterious, in fact, that some ancient civilizations directly worshipped its mystical properties and saw their dreams as ways to commune with gods, see the future, or visit loved ones past. Throughout the centuries, theoretical connections between brain activity and the necessity of sleeping were made, but not concretely proven. However, 20th century medical advancements began to open the door toward a greater understanding of the human mind and why we sleep.

EEGs Reveal the Active Brain

In 1924, at the age of 51, German psychiatrist Hans Berger recorded electrical brain activity in a human being for the first time at Jena’s University Hospital. Prior to his tests, studies had only been conducted on animal subjects. His research showed that the sleeping brain is not turned “off,” but instead has specific, repetitive and predictable electrical patterns, or stages. Berger also built the electroencephalograph (or EEG, a device that measures electrical activity in the brain), an invention that was later called “one of the most surprising, remarkable, and momentous developments in the history of clinical neurology” (Child's Nervous System, vol. 36, Mar. 2020).

REM and How We Dream

Nearly three decades later, in 1953 – the same year that James Watson and Francis Crick discovered the double helix structure of DNA – University of Chicago scientist Eugene Aserinksy (along with his mentor Nathaniel Kleitman) published a short, two-page research paper. The university would remain at the forefront of sleep research for decades to come, and their findings would challenge and guide the way we think about sleep and dreaming for the next 50 years (Smithsonian Magazine, October 2003).

According to sleep historian Michael Silber in Sleep (Oxford Academic, Jan. 2024), Eugene Aserinsky's REM investigations grew out of work assigned by Nathaniel Kleitman that ultimately led to the landmark 1953 discovery of REM. Aserinsky first applied electrodes to his test subject’s head (which happened to belong to his 8-year-old son) and connected them to an Offner Dynograph brain-wave machine. He asked the boy to move his eyes up and down and left to right to establish a baseline. The machine’s ink pens created corresponding readouts as the boy moved his eyes as instructed (not unlike the recognizable readouts of a lie detector test). Next, his son fell asleep, and Aserinsky waited. Later into the night, the pens began to move again in the same patterns as before. He checked in on his son with the expectation of seeing him awake and alert, but he was still fast asleep (Smithsonian Magazine, October 2003).

He and Kleitman continued tests with 20 adults and discovered that the periods of “rapid, jerky eye movements” happened in cycles throughout the night, along with “low amplitude, regular frequency EEG activity” and fluctuations in both breathing and heart rates. The 1953 and 1955 REM-sleep studies demonstrated recurring periods of rapid eye movements during sleep that were frequently associated with vivid dream reports and distinctive physiological activity (Sleep, vol. 47, no. 1, Jan. 2024).

Smithsonian Magazine has described REM sleep as so distinct from both wakefulness and non-REM sleep that some researchers have referred to it as a “third state of being.” The connections made between REM, dreaming and sleep health were so fundamental, in fact, that it led to a new scientific discipline called “sleep medicine”: the study, diagnosis and treatment of sleep disorders (Brown, Smithsonian Magazine, Oct. 2003; Dement, Journal of Clinical Sleep Medicine, vol. 1, no. 1).

A Breakthrough in Sleep Health

The “father of sleep medicine,” Dr. William C. Dement joined Aserinksy and Kleitman in the 1950s in Chicago as they continued their investigations. From there, he went to New York to conduct studies in a “sleep clinic” he created at his Manhattan apartment, where he discovered that abnormal REM sleep was a symptom of narcolepsy. He opened a narcolepsy clinic at Stanford University in the 1960s and founded one of the world’s first clinics dedicated to understanding and treating sleep disorders a decade later. In 1975, he helped establish the American Association of Sleep Disorder Center (now the American Association of Sleep Medicine), where he served as president for the institution’s first 12 years (American Academy of Sleep Medicine, 2020).

While with the AASM, in 1977, Dement and his colleague Mary A. Carskadon created the Multiple Sleep Latency Test, a diagnostic tool still in use today that measures the amount of time that’s elapsed from the start of a daytime nap period until the first signs of sleep. A touchstone in helping people overcome sleep-related issues, the test provides a quantifiable method to measure daytime sleepiness and is still considered the most reliable way to test for narcolepsy. By studying “sleep latency” and potential abnormalities in the start of REM, doctors can use the test to identify a multitude of sleep disorders and successfully treat them. A patient’s brain waves, muscle activity, and eye movements are monitored and recorded during the 7-hour test that can be completed within one day, in addition to an overnight observation (Cleveland Clinic, updated July 23, 2024).

Additionally, the invention of the CPAP machine to treat sleep apnea in 1981 by Dr. Colin Sullivan was a turning point in addressing a chronic and detrimental sleep issue (University of Sydney Faculty of Medicine Online Museum and Archive; The Lancet, Apr. 30, 2011).

Sleep Deprivation & Mortality

A founding member of the Sleep Research Society, Psychology professor Allan Rechtschaffen held a tireless career at the University of Chicago that began in the 1950s, studying dreams, sleep cycles and disorders alongside his contemporaries Aserinksy, Kleitman, and Dement. For four decades, he conducted studies on humans and animals that helped shed light on the connection between sleep and the body’s ability to heal and thrive (Dement, Journal of Clinical Sleep Medicine, vol. 1, no. 1). In 1968, he co-authored the first standardized manual for identifying and scoring sleep stages, where sleep was divided into REM plus four non-REM states based on brain wave patterns (University of Chicago News, December 2021).

His best-known experiment took place in 1983 and focused on sleep deprivation, using rats as test subjects. When the experimental rats started to sleep, a disk below them rotated, disrupting their attempted slumber. The control rats were allowed to sleep when the other rats were forced awake and their own disk was not moving beneath them (Journal of Clinical Sleep Medicine, vol. 1, no. 1, 2008). The test rats overate but still lost weight and quickly began to wither away, were unable to maintain a consistent body temperature, developed skin lesions, and eventually perished. (And as a result, animal rights routinely protested his testing practices). (New York Times, December 2021)

Rechtschaffen's sleep-deprivation experiments demonstrated severe physiological consequences of prolonged sleep loss in laboratory animals and became foundational studies in sleep research (Dement, Journal of Clinical Sleep Medicine, vol. 1, no. 1; Wood, University of Chicago News, Dec. 13, 2021).

Although his tests showed conclusively that sleep is needed for survival, linking the deprivation of sleep to metabolic breakdown and mortality, the unanswered reasons about why we sleep and the biological function of sleep continuously plagued Rachtschaffen, even past his retirement from the University in 2001 (University of Chicago News, December 2021).  Sleeping puts all species into an inactive and vulnerable state that seems counterproductive to evolution and survival.

In his words: “We have a lot of leads about what the function of sleep might be. But we haven’t nailed it down. So that a third of our lives still remains, for the most part, a mystery” (New York Times, December 2021).

As the scientific community began to uncover mounting evidence surrounding the importance of sleep for health, cognition and endurance, it further solidified what many had realized throughout history from their personal experiences: healthy sleep plays a critical role in physical health, cognitive performance, and overall quality of life. Naturally, in the last 25 years, as sleep continued to remain a priority for individuals all over the world, new technologies have provided both increased relief for common sleep issues and new challenges.

FAQs

Who discovered REM sleep?

REM sleep was discovered by Eugene Aserinsky at the University of Chicago in the early 1950s while working under sleep researcher Nathaniel Kleitman. Their landmark work revealed recurring periods of rapid eye movement linked to dreaming (Silber, Sleep, vol. 47, no. 1, Jan. 2024).

Why was the invention of EEG important?

EEG allowed scientists to observe electrical brain activity in real time and revealed that the sleeping brain remains highly active rather than shutting down during sleep (Millett, Child's Nervous System, Mar. 2020).

Who is considered the father of sleep medicine?

Many historians credit Dr. William C. Dement with helping establish modern sleep medicine through his pioneering work in REM sleep research, narcolepsy, and sleep-disorder clinics.

Why were Allan Rechtschaffen's experiments important?

His sleep-deprivation studies provided compelling evidence that prolonged sleep loss produces severe physiological consequences and demonstrated that sleep is essential for survival (Wood, University of Chicago News, Dec. 13, 2021; Dement, Journal of Clinical Sleep Medicine, vol. 1, no. 1).

What is the Multiple Sleep Latency Test?

The Multiple Sleep Latency Test (MSLT) measures how quickly a person falls asleep during scheduled daytime nap opportunities and remains one of the primary diagnostic tools for narcolepsy and excessive daytime sleepiness.


Sources
Millett, David. "The Inventor of Electroencephalography (EEG): Hans Berger (1873–1941)." Child's Nervous System. March 5, 2020. Published by Springer Nature. https://link.springer.com/article/10.1007/s00381-020-04564-z Historical review discussing Hans Berger, the invention of EEG, and its significance for neuroscience.

Brown, Chip. “The Stubborn Scientist Who Unraveled a Mystery of the Night.” Smithsonian Magazine, October 2003. Published by Smithsonian Institution. https://www.smithsonianmag.com/science-nature/the-stubborn-scientist-who-unraveled-a-mystery-of-the-night-91514538 This feature chronicles Eugene Aserinsky's discovery of rapid eye movement (REM) sleep at the University of Chicago, his experiments involving his son Armond, and the profound impact of REM research on the scientific understanding of dreaming and sleep medicine.

Silber, Michael H. "Who Discovered REM Sleep?" Sleep. Volume 47, Issue 1. January 2024. Published by Oxford Academic and the Sleep Research Society. https://academic.oup.com/sleep/article/47/1/zsad232/7259816 A comprehensive historical review of Aserinsky, Kleitman, Dement, and the discovery of REM sleep.

American Academy of Sleep Medicine. “In Memoriam: Sleep Pioneer and Founding President Dr. William C. Dement.” Published June 17, 2020; updated April 21, 2025. Published by the American Academy of Sleep Medicine. https://aasm.org/in-memoriam-sleep-pioneer-founding-president-william-bill-dement This institutional biography reviews Dement's contributions to REM-sleep research, narcolepsy studies, development of the Multiple Sleep Latency Test, sleep-disorders clinics, and the establishment of modern sleep medicine as a medical specialty.

Cleveland Clinic. “Multiple Sleep Latency Test (MSLT): What It Is & Procedure.” Medically reviewed and updated July 23, 2024. Published by Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/multiple-sleep-latency-test-mslt This clinical overview explains that the MSLT measures how long it takes a person to fall asleep and how quickly REM sleep begins during a series of daytime naps. The test is used to evaluate excessive daytime sleepiness and diagnose conditions such as narcolepsy and hypersomnia.

Kirby, Tony. “Colin Sullivan: Inventive Pioneer of Sleep Medicine.” The Lancet, vol. 377, issue 9776, April 30, 2011. Published by Elsevier. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2811%2960589-8/fulltext This historical profile describes Sullivan's pioneering work in sleep medicine and the development of positive airway pressure therapy that transformed treatment for sleep apnea worldwide.

University of Sydney Faculty of Medicine Online Museum and Archive. “Sullivan, Colin Edward.” Published by the University of Sydney. https://www.sydney.edu.au/medicine/museum/mwmuseum/index.php/Sullivan,_Colin_Edward This institutional profile documents Sullivan's invention of nasal CPAP technology and his role in establishing some of the earliest sleep-disorder laboratories and sleep-apnea treatment programs.

Wood, Matt. “Allan Rechtschaffen, Sleep Research Pioneer, 1927–2021.” University of Chicago News, December 13, 2021. Published by the University of Chicago. https://news.uchicago.edu/story/allan-rechtschaffen-sleep-research-pioneer-1927-2021 This biographical article reviews Rechtschaffen's pioneering research on REM sleep, sleep deprivation, narcolepsy, sleep-stage scoring, and his landmark findings demonstrating that sleep is essential for survival.

Kolata, Gina. “Allan Rechtschaffen, Who Studied Sleep and Its Absence, Dies at 93.” The New York Times, December 17, 2021. Published by The New York Times Company. https://www.nytimes.com/2021/12/17/science/allan-rechtschaffen-dead.html This obituary examines Rechtschaffen's influential sleep-deprivation experiments, his work on REM and non-REM sleep, and his lifelong pursuit of understanding the biological purpose of sleep.

Dement, William C. “History of the Development of Sleep Medicine in the United States.” Journal of Clinical Sleep Medicine, vol. 1, no. 1. Published by the American Academy of Sleep Medicine. PMCID: PMC2413168. https://pmc.ncbi.nlm.nih.gov/articles/PMC2413168 This historical review documents the emergence of modern sleep medicine and discusses Allan Rechtschaffen's landmark sleep-deprivation experiments, which demonstrated that prolonged sleep loss in laboratory animals produced severe physiological deterioration and ultimately death, helping establish sleep as a biological necessity for survival.