Mapping the Darkness: The Visionary Scientists Who Unlocked the Mysteries of Sleep 
by Kenneth Miller.
Oneworld, 330 pp., £18.99, October 2023, 978 0 86154 516 2
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Whydo we sleep? The habit is pretty much universal among animals, though it takes a wide variety of forms. Many hibernate; a dolphin sleeps with half its brain at a time, so it can keep surfacing for air; Arctic reindeer continue ruminating while in non-REM sleep; and the Antarctic chinstrap penguin, we learned last year, fits thousands of four-second ‘microsleeps’ into the course of a day. Yet there is still no scientific consensus on exactly what function sleep fulfils, why it’s so universal, or why it’s important enough to outweigh the obvious evolutionary disadvantage of rendering animals temporarily defenceless against danger.

It was this trouble making sense of sleep in Darwinian terms which, in Kenneth Miller’s account, marginalised the topic of sleep in medical science until the 20th century. There was rather more investigation of these questions earlier than he implies, especially in Germany, but it’s a striking fact that a hundred years ago there wasn’t a single full-time medical specialist in the subject anywhere. Across the life sciences in the 19th century, sleep was generally considered to be a vestige of our deep evolutionary past with no present value. Given its obvious disadvantages so far as economic productivity is concerned, there was much speculation that modern medicine would discover a way to reduce the need for it, or even eliminate it altogether. Sleep science, once it emerged, followed the shifting currents of 20th-century physiology and biomedicine. Each new paradigm brought fresh discoveries, created new mysteries and adjusted the focus of research, yet the fundamental questions remain unanswered.

Research was driven from the beginning by practical considerations. During the Progressive Era in the United States of the early 20th century, the expanding domains of public health and statistical analysis revealed that sleep deprivation was an endemic problem among the working populations of the industrial world. In 1909 the engineer Frederick Winslow Taylor introduced the principle of ‘time and motion’ studies to analyse labour productivity. The British psychologist William McDougall and the young W.H.R. Rivers devised laboratory tests to measure fatigue, which correlated with reduced hours of sleep and revealed rates of chronic insomnia far higher than anticipated.

The causes of sleeplessness were obvious and largely intractable: the spread of electric lighting had cut into the hours of darkness and made it possible to extend workers’ shifts beyond the interval between dawn and dusk. Labouring to the rhythms of the factory and the economic machine, rather than nature or the human body, led to a state of exhaustion and burnout which the US neurologist George Miller Beard diagnosed as ‘neurasthenia’. Beard defined the condition as a depletion of nervous energy and explained it by analogy to an electrical current: when a circuit is overloaded with light bulbs, it eventually reaches a point where ‘the amount of force is insufficient to keep all the lamps actively burning.’

By the 1920s, after the discovery of hormones such as adrenaline, explanations for brain activity shifted from the electrical towards the chemical. The discovery that lactic acid accumulates in exhausted muscles prompted the theory that certain glandular secretions, or ‘hypnotoxins’, might build up over time when there was insufficient sleep to process or absorb them. The French physician Henri Piéron, who published a detailed monograph on sleep in 1913, deprived dogs of sleep for long periods before injecting their blood, puréed brains and cerebrospinal fluid into other dogs; he noted that some subsequently became sleepy, but he was unable to identify the chemicals that might be implicated. In 1916 the mysterious epidemic of encephalitis lethargica or ‘sleepy sickness’, which left sufferers in a permanently comatose state and, post mortem, with distinctive brain tissue damage, suggested to some that there might be a dedicated ‘sleep centre’ in the brain.

These and other hypotheses, including Ivan Pavlov’s claim that sleep was an inhibitory response designed to protect nerve cells from overwork and deterioration, inspired the first of the scientists around whom Miller structures his history. Nathaniel Kleitman had escaped a Russian pogrom on the eve of the Great War and was studying physiology at the University of Chicago when, in 1922, he decided to specialise in the study of sleep. In 1925 he set up the first sleep laboratory, obtaining a grant from the Rockefeller Foundation on the promise of discovering cures for common sleep disorders including insomnia and narcolepsy. Kleitman too used dogs for his experiments, since they were thought to sleep in ways similar to humans: he removed the cortical layer of their brains and noted that their sleep patterns became jumbled as a result. He also ran human trials, charting his subjects’ physical movements, temperature and depth of sleep over the course of the night.

The experiment that brought sleep science to global attention was one that Kleitman performed on himself. In 1938 he and a graduate student, Bruce Richardson, descended into the depths of the Mammoth Cave in Kentucky, where they spent the next 32 days a quarter of a mile from the nearest chink of daylight, maintaining an artificial sleep-wake cycle of 28 hours. They kept time with alarm clocks, took their temperatures regularly, grew beards, stashed chamber pots in the cave recesses, ate fried chicken and smoked cigarettes, all on a rigid timetable of nineteen hours awake followed by nine asleep.

They emerged a month later to be greeted by a scrum of film crews and reporters who had assembled to watch them take their first steps into the light and quiz them about their experience. Kleitman told them that the experiment had been a perfect success and that he had slept wonderfully. In fact the results were inconclusive: Richardson had adapted his sleep patterns to the 28-hour cycle within two weeks but Kleitman had been unable to do it. His subsequent book, a 638-page monograph titled Sleep and Wakefulness as Alternating Phases in the Cycle of Existence, became the bible of the new field, but his work didn’t much impress the Rockefeller Foundation: it withdrew his funding, pronouncing his findings ‘negligible without being false or useless’. Other scientists maintained that sleep was a trivial function, comparable in significance to vestigial organs such as wisdom teeth, tonsils or the appendix. At Columbia University, the psychologist H.L. Hollingworth proposed that if we simply reduced the time we spent sleeping by five minutes every two months, it should be possible to stop sleeping altogether within sixteen years.

The first real scientific breakthrough came with the invention of technology that transposed the activity of the brain into visible data. In 1924 the German psychiatrist Hans Berger, who had spent years trying to measure electrical activity in exposed dogs’ brains, placed electrodes on the scalp of a student whose skull had been cut away to remove a brain tumour and succeeded in tracing the oscillations of the brain’s electric activity with a galvanometer. Berger’s electroencephalogram, or EEG, created what he called ‘a kind of brain mirror’, which revealed two distinct, alternating brainwave frequencies he named alpha and beta waves.

After a long process of refinement and many experiments, including on Albert Einstein, Berger reported in 1938 that the sleeping brain went through several different cycles, not just alpha and beta but also a slower wavelength he named delta which characterised deep sleep. Kleitman and his new assistant, Eugene Aserinsky, used the EEG to investigate narcolepsy and to study the phenomenon of rapid eye movement in certain phases of sleep. The wandering of eyes under their lids had typically been seen as a sign that a fitful sleeper was on the point of waking, but Kleitman and Aserinsky showed that REM was different: it was a recurring phase of the sleep cycle, which indicated heightened cortical activity and that the sleeper was dreaming. Sleep, it turned out, was not one state but two, as different from each other as sleep is from waking.

The discovery of the REM state brought dreaming into the purview of physiology for the first time. Kleitman’s latest recruit, William Dement, who joined his Chicago team in 1952, was fascinated by Freud’s theory that dreams might function as a safety valve for libidinal energy that otherwise risked erupting into waking life as psychosis. The discovery of REM supported Freud’s contention that sleep was not simply oblivion but a state of intense cerebral activity, in which the day’s activity was digested and reconfigured by preconscious or subliminal stimuli.

The 19th century may have produced little scientific work on sleep, but there was a vast and sprawling pre-Freudian literature on dreams, much of it entangled with other mental phenomena – hallucinations, delusions, hypnagogia, dissociation, clairvoyance – that were considered to be forms of ‘dreaming while awake’. Dement and others hoped to demonstrate that dreams were related to Freud’s ‘subsidiary and unnoticed’ impressions of waking life by showing their subjects slides and subliminal messages before sleep. But clear connections to dream content were elusive. By the late 1950s the reputation of their research suffered by association with the debunked claims about subliminal messaging in The Hidden Persuaders, Vance Packard’s sensational exposé of covert advertising techniques. By this time, too, the biophysical turn in psychiatry was drawing sleep research away from psychoanalytic theory and towards the frontiers being opened up by drugs and neurotransmitters.

In 1959 Peter Tripp, a radio DJ in New York, decided to stay awake for two hundred hours to raise money for charity. Tripp set himself up in a glass booth in Times Square, monitored by sleep researchers, where he rapped and span records for two days and nights before his mental state began to unravel. He developed a disturbing thousand-yard stare, became angry and profane, hallucinated crawling bugs on his clothes and by the 170-hour mark was accusing the sleep scientists of poisoning his food and framing him for unspecified crimes. In the end he fled the experiment with several doctors in pursuit. When he did finally manage to sleep, he was wired up to Dement’s EEG machine and had one of the longest REM phases ever recorded. Dement theorised that Tripp had been suffering from a build-up of ‘REM pressure’, an update on the notion of hypnotoxins, but his paranoia and disordered thinking weren’t replicated in other trial subjects. It emerged later that Tripp had spent the last sixty hours of the experiment dosing himself with Ritalin, and his experience was perhaps more plausibly explained as acute drug-induced psychosis. It also resulted in a long-term personality change: he began to believe that he was not Peter Tripp but an impostor, and he and his wife divorced.

This highly publicised tragic episode marked an end to the tradition of heroic self-experiment that had begun with Kleitman’s descent into the Mammoth Cave, and hastened the shift to laboratory-based neuroscience. In 1963 Dement moved to California and set up the Stanford Sleep Research Centre, which would become the model for the modern sleep clinic. Its site in Menlo Park Veterans’ Administration Hospital, where Ken Kesey had recently been a volunteer in psychedelic trials and researched One Flew over the Cuckoo’s Nest, was a focus for the civil rights movement, and Dement, a jazz musician in his spare time, became aligned with its progressive currents and acted as adviser to the Stanford Black Students’ Union.

The centre’s initial focus was on REM sleep, its role in narcolepsy and the changes in brain chemistry involved in it. Dement’s theory was that its biological value peaked in newborn babies, diminishing after infancy. But new frontiers in brain research were opening rapidly. Links were established between sleep and levels of the neurotransmitter serotonin and, most significant, the circadian sleep cycle was found to be set by a genetic mechanism and regulated by secretions from the pineal gland. Circadian rhythms, or the ‘biological clock’, ran slightly longer than a terrestrial day, and varied between individuals. The well-worn observation that there were ‘morning people’ and ‘night people’ now had scientific validation.

The Stanford Centre expanded its networks of funding and influence by cultivating a focus on sleep disorders, the same strategy that Kleitman had deployed to attract Rockefeller money in the 1930s. A new discipline of ‘sleep medicine’ emerged, focused on insomnia, narcolepsy, apnoea and other breathing disorders; ‘parasomnias’ such as sleepwalking and night terrors; and the development of sleep medications. The big breakthrough for the new field came from Australia’s first sleep laboratory, set up in 1979 by the physician and inventor Colin Sullivan and announced in 1981 in an article for the Lancet, ‘Reversal of Obstructive Sleep Apnoea by Continuous Positive Airway Pressure Applied through the Nares’. Sullivan’s CPAP device, as it became known, changed the perception of apnoea: it was no longer thought of as an obscure condition mostly afflicting obese elderly men but as a widespread and treatable disorder, which affects an estimated 24 per cent of adult men and 9 per cent of women. It also brought sleep medicine to the consumer market: sales of CPAP machines took off rapidly and helped launch the concept of ‘sleep hygiene’, transforming sleep doctoring into a lucrative medical specialism.

Another crucial step in unlocking new sources of funding was the growth of public health and epidemiology. The last of Miller’s sleep science heroes, Mary Carskadon, who began as Dement’s teaching assistant, directed a series of large population studies to investigate the role of sleep cycles and sleep deprivation in a wide range of social and medical contexts. She showed that the likelihood of fatal accidents peaked between midnight and 6 a.m., the point in the circadian cycle when alertness levels are lowest and unintended microsleeps most common. In the 1990s she also demonstrated that the biological clocks of adolescents are such that, in the early morning, ‘the students may be at school, but their brains are at home on their pillows.’ Like many sleep studies, Carskadon’s research marshalled scientific data in support of a long-recognised phenomenon, but the obvious solution she proposed – starting school later – gained little traction. We are, it seems, too wedded to our accustomed schedules for work and childcare.

Over recent decades, the physiology of sleep has become ever more complex, and the treatment of its disorders is now a major component of the medical business sector. There are more than 2500 sleep clinics in the US alone; in 2020 the size of the ‘sleep economy’ was estimated at $432 billion; this year it is expected to climb above $500 billion. That includes $25 billion for CPAP machines and $9 billion for ‘ambience optimisation’ products such as white-noise headphones and blackout curtains. There are now more than eighty diagnosable sleep disorders, affecting an estimated one in three of the global population. All this is hailed by Miller as the triumph of sleep science, though it could also be taken as evidence of the opposite: there are so many options because there is still so little scientific clarity. There is no cure for any of the disorders – insomnia, narcolepsy, apnoea – that sleep science was originally intended to address; nor is there a sleeping pill that works without suppressing natural circadian rhythms and brainwave cycles or inducing dependency.

‘The most basic questions’ about sleep, Miller concludes, ‘still lack definite answers.’ In Why We Sleep (2017), the bestselling guide to 21st-century sleep hygiene, Matthew Walker dismisses his own title in the opening pages: it has turned out to be ‘the wrong question’. But waving it away isn’t the same as answering it. Sleep, he goes on to say, has no single purpose but fulfils ‘a rich litany of functions’ and ‘dispenses a multitude of health-ensuring benefits’. The range of physiological processes influenced by sleep is vast, which means the number of potentially beneficial interventions is nearly infinite. There are countless tips, techniques and habits that can improve sleep, many of them buttressed by scientific evidence and enthusiastic media coverage: at the beginning of this year, the Wall Street Journal splashed a feature on an academic study proving that people who suffer from cold feet sleep better if they wear socks. Yet beneath the imprimatur of science, the larger picture more closely resembles the Hippocratic medicine of the pre-scientific era: a teeming marketplace of pills, herbal supplements, diets, exercise, medical devices, apps and mind cures, with remedies to suit every customer, temperament and wallet. Meanwhile, studies generate more and more evidence that sleep disorders have a genetic component, which suggests that the reach of lifestyle therapeutics must be limited.

There is much more consensus on the question of why we don’t sleep. Modern life has mounted what Miller describes as ‘an ongoing, and ever escalating, assault on sleep’: our always-on work culture, with its shifts and double jobs, ubiquitous sound and light pollution, and the blue light from screens and digital devices which throws our circadian rhythms into confusion. The ever expanding market for sleep optimisation is a response to this ever escalating assault, but consumer and lifestyle remedies remain least available to those who need them most: working people, particularly those who are also parenting, in low-quality housing and noisy urban environments across the globe. It’s hard not to notice that all these modern anxieties and pressures are essentially no different from those that led to the birth of sleep science more than a hundred years ago, in the glare of the electric light.

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