On the Invisibility of Sleep

Not sleeping is a form of torture. Without it, we die. We divert roads and close airports to protect it. But, for all its importance, do we know what sleep actually is? When we sleep, our intellect is paused. Sleep negates the very organ we use for synthesising experience as knowledge. It cannot be described while it’s happening: there can be no commentary as there is with, say, pain or emotion. Neither the conscious nor the unconscious mind can ever honestly observe: ‘I am asleep now.’ Here’s the conundrum: asleep, we cannot communicate the experience. Awake, we cannot experience it. The texture of sleep remains unknown.

In neuroscientific disciplines—that area of science that deals with the brain—sleep can be understood as a specific electrical state. The brain is an electrical organ, made up of neurons, each a tiny vector on a complex electrical network. All sleeping brains, be they infant or elderly, human or animal, exhibit notably similar electrical characteristics. Electroencephalography (EEG) uses sensitive receptors placed on the scalp to measure the summation of these billions of electrical signals and charts them side-by-side on reams of graph paper; a symphonic score of waveforms. From these lines, patterns emerge.[1] Delta waves, Theta waves, K-complexes and intricate sleep spindles are the key landmarks of sleep’s geography, identifiable among the complex background patterns. The presence and frequency of these waveforms are signatures, defining the four stages of sleep. The stages are like steps at a swimming pool: we enter at wakefulness and wade down into the depths.

Stage 1 is a period of intense drowsiness, and is a transition phase from being awake into the light sleep of stage 2. Both stages 1 and 2 are characterised by a general slowing of electrical activity in comparison to wakefulness, while stage 2 demonstrates an increase in Theta waves, K-complexes and sleep spindles. Stage 1 is the gateway into sleep: we pass through it briefly as we slip into slumber, then again on our way into and out of dreaming. If we enter stage 1 for less than a minute we will usually deny having slept. Stage 2 accounts for around half the night’s sleep.

Stage 3 is the transition from the light sleep of stage 2 into stage 4: deep sleep. In stage 3, Delta waves start to roll in rhythmic patterns and by stage 4 they are present across the whole brain. We plunge towards stage 4 upon falling asleep, but spend just 10–20 per cent of the night there. Stage 4 is believed to be a period of intense recovery. After a period of sleep deprivation, it is only the missing stage 4 sleep that the body fully replenishes; the other stages are recovered only proportionally. The reason for this is not clearly understood.

Along with the four stages of sleep is rapid eye movement (REM) sleep, also called paradoxical sleep because its electrical signature mimics that of wakefulness. We wade up through stages 4, 3, 2 and 1 to enter the REM state. In REM sleep the eyes flicker quickly, the brain is very active and dreaming is common. The body is locked into ‘atonia’, a specific paralysis that prevents us from acting out our dreams. In REM sleep, the brain maintains a level of responsiveness to outside stimuli, ignoring familiar noises—rain, traffic, a flushing toilet—but more likely to respond to a whispered name or a foot-step. If the first four stages are depths of immersion in sleep, then we float on the surface to dream. We tend to be more likely to recall our dreams if we are awoken directly out of the REM phase. Collectively, stages 1 to 4 are called non-REM sleep, and dreams in these stages are rarer and less fantastic than dreams during REM sleep.

While sleep varies subtly from individual to individual, EEG shows that the sequence and pattern of sleep’s electrical activity is universal. We begin by descending into deep sleep almost immediately and stay there for up to an hour. Climbing from these depths we rise into lighter sleep, and at this crest we may dream briefly before returning to deep sleep. These cycles of lighter-deeper-lighter sleep occur approximately every ninety minutes and get progressively shallower. In general, the third cycle drops no lower than stage 2 and lingers longer in the REM state.

A simplified hypnogram, depicting an eight-hour period of sleep.

These stages, however, are based on interpretations of a limited data set, accounting only for sleep’s electrical phenomena. While EEG can provide useful insight into the sleeping brain, it is a long way from providing a definitive map of sleep’s geography. No matter how detailed, such measurements do not reflect the breadth of the human culture of sleep, nor the depth of its history. Even when EEG is combined with apparatus measuring the motion of the eyes beneath the lids, the twitching of the body or the saturation of oxygen in the blood, we receive only quantitative data on sleep’s physical manifestations. The sleeper is unable to report on the qualitative data—the experience of sleep.

Exceptions to the usual sleeping patterns range from the extreme to the everyday. Take, for example, solo round-the-world sailors who, through necessity, sleep in bursts of around thirty minutes at a time to maintain vigilance over navigation. Or consider those hot-weather cultures that reserve an hour or two in the middle of the day for a siesta, breaking their sleep patterns into two distinct sessions. Indeed, it is possible that our preference for eight hours’ sleep is a modern Western phenomenon: the Victorians considered eight hours to be a luxury for the idle rich, and traditions of a ‘first sleep’ in the early evening followed by a ‘morning sleep’ in the small hours date back considerably further.[2]

The experience of sleep is often conflated with the experience of dreaming. But dreams are not sleep, just as sleep-talking and snoring are not sleep—they are symptoms of it. Sleeping is the state in which dreaming may occur. While dreaming concerns sections of the brain, sleep is systemic, occurring all over the brain and throughout the body’s anatomy and chemical systems. Sleep is more than just electrical signals, it is an occupation of the whole body. Hormones dictate our circadian cycle and lead us towards sleep in approximately 24-hour intervals. Our breathing and pulse change tempo; skin chemistry fluctuates; hunger is quelled. It is a complex biological pattern, and disruption can be unpleasant and undesirable. Indeed, much of science’s interest in sleep is not so much in defining and measuring its presence as its absence. It is in the investigation of not sleeping. All manner of institutes and centres exist to investigate the absence or disruption of sleep. Studies abound on sleep-related phenomena such as narcolepsy (falling asleep suddenly and unexpectedly), fatal familial insomnia and a variety of sleep disorders that induce the sleeper to walk, eat, fight or even have sex. A sub-specialty exists in respiratory medicine treating breathing disorders during sleep, such as snoring, sleep apnoea and its associated breathing apparatus. Pediatric sleep specialists assist children through various disorders more prevalent in childhood, such as night terrors, head-banging, sleep walking, even advising of the essential act of getting to sleep. Sleep hygiene is an important consideration too—not just bedbugs and clean sheets but also the importance of pre-sleep routines. There is a long history of fortunes made from developing sleeping draughts and tablets, water beds and latex pillows, magnetic underlays and electric blankets. The field of endeavour in sleep improvement is vast, but none of these ventures engages directly in the quest to know sleep.

It is, perhaps, only when sleep is lacking, prevented or otherwise disrupted that we are truly aware of its existence. In contrast to sleep, the experience of sleep deprivation is observable and knowable. It engenders intense sleepiness: an insistent tugging; a sensation of deep, dragging tiredness; like being immersed in mercury; subject to an excess of gravity; with aching teeth and heavy limbs that both seek and resist movement. And sleep deprivation has its purposes: as a torture method, it is considered ‘clean’, leaving no trace on the body while lowering the pain threshold and weakening the mind’s defences, enhancing the efficacy of other torture techniques.

The early symptoms of sleep deprivation include use of a repetitious vocabulary dependent on cliché, a flattened vocal tone and short, slurred sentences. We demonstrate a decreased ability to concentrate and increased skin sensitivity. As sleep deprivation advances, some of those human qualities of which we are generally unaware also begin to fall away. Aside from the reduction of our vocabulary, we lose our ability to recall the duration or sequence of events. We become unable to discern relevant from useless information and we obsess over small details. We grow more prone to suggestion, and as decision-making becomes increasingly lax we take greater risks. These are our ‘executive functions’ and without them we become automatons, progressively less able to act intelligently.[3] A number of significant disasters in recent human history are attributed in some part to sleep deprivation: Challenger, Chernobyl, the Exxon Valdez and (more prosaically) countless car accidents.[4] But while studying the absence of sleep, like studying its disorders, brings us closer to knowing its function, it does not allow us to know sleep itself.

Philosophy attempts to understand sleep but it too falters at the moment we slip away from consciousness. Sleep exists outside reason and deduction: unknowable from within and unknowable from without. How can we analyse its essence? What makes it different from, say, lightning? Or gravity? Broadly speaking, philosophy does not intersect with that extended period of each day when we are without thought, knowledge or morality, focusing instead on the state of wakefulness. Some phenomenologists, Edmund Husserl in particular, have attempted to integrate sleep into understanding of selfhood and our experience of identity.[5] It is during our periods of wakefulness that we participate in society, that we engage, communicate, think, and form our understanding of ourselves, other humans, and our environment. What happens to the self between these periods? Descartes contends, ‘I think therefore I am.’ Who (or indeed what) are we, then, when we sleep? The self survives sleep essentially unchanged (although proponents of psychoanalysis may disagree, with respect to the effects of dreams). With the rare (but often embarrassing) exception, we tend to awaken fully aware of who and where we are. The body may awaken slightly changed, a little taller after a respite from gravity’s pull, perhaps slightly lighter from perspiration overnight, perhaps more hung-over, perhaps a little less puffy around the eyes. But our person is not significantly different: we do not awaken with newly developed virtuosic musical talents, nor have we found a new political persuasion overnight. Our internal monologue has not acquired a foreign accent, nor begun obsessing over the natural logarithm. The self exists smoothly, through linked intervals of wakefulness, argues Husserl, punctuated by periods of neutral sleep.[6] But its nature during those intervals is unknown, and without that self are we even human? Perhaps sleep simply takes us closer to our animal core. How can we know?

Through its very neutrality sleep is overlooked, despite its daily presence. It is so habitual, so frequent, so routine, that we cease to notice it. We may enquire in the morning, ‘How did you sleep?’ but following the acceptable response, ‘Well, thanks,’ we tend not to follow this line of questioning further. Discussions of dreams, sleep phenomena, disturbed or absent sleep, however, are more commonly pursued. We do not seek to discuss normal sleep, to unpick its qualities or its substance, nor to meditate upon its pleasurable nature. Yet how delightful is a good night’s sleep! How buoyant, how translucent, how crisp! It is hand-blown glass, a jellyfish, a wet window, an exhaled breath.

There is, however, a strong ambivalence here. While we value sleep and dread the lack of it, we relegate it to the fringes of our (Western) social structure. Sleep is conducted in private, nesting the sleeping body and protecting it in its period of such vulnerability. Submerged for much of the night in stages 2 to 4 of sleep, with our attention turned away from external stimuli, our body is left without the protection of its vigilant watcher. Like animals, we have always sought a safe place for sleep, whether in a cave, a shelter or simply by the fireside. This need for protection forms the fundamental role of the dwelling. Homes provide a space to sleep—all other activities can be (and prehistorically were) done in the public sphere. By crude definition, homelessness is at its root the lack of a place to sleep privately. Western cultural mores require us to hide ourselves away to sleep, and then enforce this through designing our public spaces to repel the sleeper. Bus stops take the form of angled seats, park benches are fitted with a central armrest—like two armchairs pushed together—to deter anyone but a contortionist from lying down. Sleeping is tolerated in certain sanctioned spaces (such as in waiting rooms, libraries or on public transport) but is otherwise strongly discouraged. Sleep is wilfully overlooked. We close our eyes to it, push it into private space and avoid discussing it. We will its invisibility.

And sleep is invisible because we do it in the dark. We are part of the animal kingdom, and by our own biology we are slaves to our circadian cycle. Though we may bend with the passing current of culture that flows in the direction of a 24-hour society, we follow the dictates of our 24-hour body clock. Night-time is for sleeping. During the dark hours, when most of us are in our beds, those industries that continue to operate at night are subject to strict controls. Night freight travels along city bypasses; use of air brakes is forbidden in built-up areas. The sirens of emergency vehicles are silenced. Trains run express. Even busy international airports are placed under curfew. Local councils ban noise in neighbourhoods and on building sites. Society legislates to protect sleep at night, and in doing so keeps it invisible and private. With dawn comes life—the shared life of a society that has spent the past eight hours trying to get some rest.

Sleep is also unwritten. It occurs between the chapters of a book. Our hero falls asleep at the end of one chapter, and awakens on the next page to a new narrative. In the exception, narrating sleep provides opportunity for the author to take an introspective turn. Marcel Proust writes pages of sleep in his In Search of Time Past, allowing the character to ruminate before passing into stage 1. Sleep is the vehicle, not the subject. In So long and thanks for all the fish, Douglas Adams digresses from his story to acknowledge that he, like most authors, had not included ‘the whole truth’ of his narrative but had instead ‘cut out all the tedious happenstance’. Were he to recount in full the action of his protagonist, Arthur Dent, the reader would be forced to endure such narration as: ‘… he turned out the light and within a minute or so more was asleep. It was dark. He lay on his left side for a good hour. After that he moved restlessly in his sleep for a moment and then turned over to sleep on his right side. Another hour after that his eyes flickered briefly and he slightly scratched his nose, though there was still a good twenty minutes to go before he turned back on to his left side. And so he whiled the night away, sleeping.’ ‘It’s guff,’ Adams concedes. ‘It doesn’t advance the action … You don’t, in short, want to know.’[7]

Sleep is without story. Sleep is the break in the story. It is, by its very definition and application, a period of rest. What is there to write about sleep? What could we ever write that would illuminate it? Good, plain sleep is invisible. It harbours no narrative and demands no investigation. This essay, which attempts to know sleep, cannot advance its epistemology. Sleep reposes, allows the brain to take leave, rests the body, pauses the personality. And knowledge, like sleep, is behaviour of the brain; so it seems only right to me that we be excluded from knowing that very moment in which knowledge itself is at rest.

Notes
1. For an explanation of sleep stages in layperson’s terms, see Jim Horne, Sleepfaring: A Journey through the Science of Sleep, Oxford University Press, New York, 2006; or Jacob Empson, Sleep and Dreaming, 3rd edn, Palgrave Macmillan, Houndmills, Basingstoke, Hants, 2002. Back to article

2. Horne, Sleepfaring, pp. 186–7. Back to article

3. For more on the effects of sleep deprivation, see Darius Rejali, Torture and Democracy, Princeton University Press, Princeton, NJ, 2007, p. 468. Back to article

4. Horne, Sleepfaring, pp. 72, 88. Back to article

5. Husserl’s original text on this topic was entitled Späte Texte über Zeitkonstitution, 1929–34, published as Die C-Manuskripte, ed. Dieter Lohmar, Springer, New York, 2006. Back to article

6. Manfred Geier discusses Husserl’s ideas on the sleep’s phenomenology in ‘Sleep as a temporal bridge: on the phenomenology of the sleeping consciousness’ in Helga Raulff, Michael Dorrmann, James Peto and Ken Arnold (eds), Sleeping and Dreaming, Black Dog Publishing, London, 2008, p. 52. Back to article

7. Douglas Adams, The Hitchhiker’s Guide to the Galaxy, Heinemann, London,1991, pp. 548–9. Back to article