Sleep before the laboratory

The history of sleep medicine involves changing explanations of an everyday experience as well as changing ways to investigate illness. Philosophical accounts, electrical recordings, experimental awakenings and respiratory interventions supplied different kinds of evidence. The selected episodes below trace how sleep became an object that researchers could divide into states, model over time and connect with specific physiological disturbances.

In On Sleep and Sleeplessness, written in the fourth century BCE, Aristotle treated sleep as a bodily phenomenon shared by animals. He connected it with sensation, digestion and the movement of bodily heat, placing the primary organ of sensation in the region of the heart. These were historical explanations, not accounts accepted by modern physiology. Nevertheless, his questions distinguished the occurrence of sleep from the experience and recollection of dreams. The text documents one influential intellectual tradition; it cannot establish how everyone in antiquity understood or experienced sleep. Aristotle, translated by J. I. Beare.

Making sleep electrically visible

Electrical recording changed the evidence available to sleep researchers. In 1937, Alfred L. Loomis, E. Newton Harvey and G. A. Hobart published an investigation distinguishing five sleep states through patterns of human brain potentials. Their observations showed repeated changes during the night, rather than a single uniform condition. They also reported that bodily movement and changes in electrical state did not always coincide.

The historical significance lies in that separation between outward appearance and recorded physiology. A motionless sleeper could undergo changes that an observer could not identify by watching alone. Conversely, movement did not necessarily mean that the underlying recorded state had changed. Their classification should be understood as an early research system, rather than silently equated with later sleep-stage terminology. Instruments made new distinctions possible, but researchers still had to decide how to classify the traces and interpret their meaning. Loomis, Harvey and Hobart, 1937.

Rapid eye movements and the study of dreams

Eugene Aserinsky and Nathaniel Kleitman’s 1953 report described recurring periods of eye movements during sleep and accompanying physiological changes. Their experimental awakenings connected these periods with reports of dreaming. This research helped establish rapid eye movement, or REM, sleep as a distinct subject of investigation and supplied a practical way to relate recorded bodily events to subjective experience. Aserinsky and Kleitman, 1953.

The methodological distinction matters: an electrical or eye-movement record is not itself a record of a dream. Researchers obtained dream evidence by waking participants and asking them what they remembered. Association between a physiological period and reported experience therefore depended on both measurement and testimony. Historically, this makes the discovery more informative than a simple story about finding a single biological switch for dreaming. It opened questions about recurring sleep states while leaving the interpretation of conscious experience dependent on the methods used to investigate it.

Breathing disorders and a therapeutic turning point

Research on breathing during sleep provided a particularly direct connection between laboratory observation and treatment. In 1981, Colin Sullivan, F. G. Issa, Michael Berthon-Jones and Lorraine Eves reported the use of continuous positive airway pressure delivered through the nose in five patients with severe obstructive sleep apnoea. Their report showed that maintaining pressure in the airway could prevent the obstruction observed during sleep. Sullivan and colleagues, 1981.

This was a small clinical report, and its historical importance should not erase that limitation. It demonstrated a physiological intervention in selected patients; it was not evidence that every complaint of poor sleep had the same cause or required the same treatment. As a historical episode, it illustrates how sleep investigation could identify a specific mechanism and test an intervention against it. The description here concerns the development of medical knowledge and does not provide instructions for treatment.

Regulation, interpretation and legacy

Another important development concerned the timing and regulation of sleep. Alexander Borbély’s 1982 two-process model distinguished a homeostatic process associated with sleep and waking history from a process governed by the circadian pacemaker. The model offered a framework for understanding why sleep timing cannot be explained solely by how long someone has been awake. Its authors’ later reappraisal described applications to fatigue, performance and individual differences. Borbély, 1982; Borbély and colleagues, 2016.

Taken together, these studies suggest a history of complementary approaches rather than one discovery replacing every earlier question. Electrical classification addressed changing states within sleep; experimental awakenings investigated remembered experience; airway intervention tested a respiratory mechanism; and mathematical modelling addressed regulation across time. This is an interpretation of the selected evidence, not a claim that these episodes exhaust the field’s history. Their enduring significance is the insistence that sleep has measurable organization while also requiring careful distinctions between observation, explanatory models and the experiences reported by sleepers.

Historical evidence and further reading