They sleep for about 12 hours a night, although the young ones need more time in the sack. Caffeine keeps them awake and antihistamines cause drowsiness. Sleep deprivation makes learning new skills difficult the next day and afternoon naps make up for it. Some are insomniacs. This is what sleep scientists are discovering about drosophila, the little red-eyed fruit fly usually found hovering above bowls of blackening bananas.
And drosophila are not the only creatures sleeping. From unicellular organisms up, all animals show patterns of rest and activity, and most of it resembles sleep. Lions snooze for 18 hours a day, giraffes doze standing up for a measly three and a half hours a night. Birds catnap on the perch. Dolphins sleep unihemispherically, with one side of the brain at a time – literally with one eye open and the other asleep.
Until the 1950s, sleep was considered just a way of killing time, a possible bad habit and an optional activity, something to be indulged in if there was nothing else of interest going on. From an evolutionary view, this does not make sense. Sleeping animals are highly vulnerable, so if the process is not essential, why do it at all?
When, in a gruelling series of experiments, scientists observed that rats deprived of sleep keeled over and died after two weeks, sleep began to appear less optional.
A family in Italy was described with a genetic disorder that manifested in the fourth decade of life with a complete inability to sleep. Hypertension, sweating, hallucinations and death followed within two years.
And in 1953 when Nathaniel Kleitman, the founding father of sleep science, shone a torch on a sleeping subject's face and noticed eye movements beneath the closed lids, rapid eye movement – or REM – sleep was discovered.
The sleep process began to appear less inactive than originally suspected. Electroencephalography, conducted by attaching electrodes to the head to reveal brainwaves, confirmed that sleep is a highly structured, active brain state, with mysterious and essential biological functions.
To learn more about how we spend a third of our lives, I submit myself to a sleep study, called polysomnography, courtesy of Constantiaberg Mediclinic and Dr Irshaad Ebrahim, a psychiatrist who specialises in sleep disorders.
I have no specific sleep complaints, but I am curious to learn how sleep data is gathered and I have often wondered how people sleep at all under such close surveillance.
A rather ordinary hospital bed in a quiet ward will be mine for the night. In the next room is a young woman who, according to her accompanying mother, will sleep for an entire weekend if left undisturbed.
Petro Daries, the nurse on duty, begins gluing electrodes to my scalp.
"You're going to hate me afterwards," she says. "This stuff is impossible to get off."
After attaching electrodes to the skin overlying the frontal, occipital and temporal lobes of my brain, she tapes sensors to my jaw and cheekbones. Electrodes are also strapped to my calves.
"To check for teeth grinding," Petro explains, "and restless legs."
A belt around my waist will transmit my sleeping position, another around my chest will record my heartbeat. A peg with a glowing red light is clipped to my finger to monitor the oxygen content of my blood, and an insect-like device taped to my upper lip – its antennae extending into my nostrils – will measure my breathing. The set-up process takes nearly an hour.
After plugging the wires from the electrodes on my body into what looks like a small, old-time telephone exchange, Daries informs me that she will be back at five the next morning, and wishes me good night. A Bible lies on the bedside table. Sleep aid or solace for the distressed, I wonder.
Beneath the gaze of a pair of wall-mounted cameras, I read a little about sleep disorders. In spite of some performance anxiety and the ticklish insect on my upper lip, and the belts, wires and gobs of glue, I feel surprisingly drowsy after a few pages and I turn off the light. As I drift away, the electrodes transmit my brain waves to the monitor.
The resulting graph of normal sleep, a hypnogram, resembles a series of descending and ascending staircases.
The first stage of sleep is very light – barely sleep at all.
Stage two is proper sleep, but is still light enough to wake easily in response to a noise. In stage three, the brain produces delta waves in long, rhythmic bursts.
Stage four, the deepest level of sleep, is associated with slow brain waves. It is difficult to awaken from stages three and four, and people doing so feel groggy and unable to think clearly for some time afterwards, a condition labelled sleep inertia.
From stage four, sleep returns to stages three and two, and then to REM sleep. In this phase of sleep, the body is paralysed, and the brain and closed eyes become very active as dreaming begins. Breathing
and heart rate become irregular. After a period of REM, the brain descends once again to deeper levels of sleep.
Throughout the night this process repeats itself in cycles of roughly 90 minutes. As the night progresses, time spent in deep sleep diminishes, and the proportion of REM sleep increases. About a quarter of normal sleep is spent in REM and disruption of the process has serious consequences.
Gosia Lipinska, a neuropsychologist and sleep researcher at the University of Cape Town, explained to me in a prior interview that those areas of the brain that are active during the processing of memories while awake are also active in REM sleep, but the brain centres responsible for reality awareness and consciousness are turned off. Brain centres controlling emotion are highly active.
This explains the strange nature of our dreams, most of which also tend to be unpleasant or disagreeable and commonly feature themes of arriving late for a test, chase scenes, terrible illness or crumbling tooth loss.
According to Lipinska, memories deemed worthy of keeping long-term – usually because they are associated with emotions – are strengthened during slow-wave sleep and then laid down for long-term storage during REM sleep.
The part of the brain responsible for taking on new memories is wiped clean, ready for a new day.
"We have only one brain, and we need to both experience life and process it," says Lipinska. "Sleep allows time for that processing to take place."
As the night wears on, I wake several times to see the red eye of the camera staring down at me. These awakenings register on the hypnograph as steep spikes as I slip in and out of consciousness.
At five in the morning, Daries turns on the light.
"You slept well," she says with a pleased smile, "you even reached stage four."
I feel oddly flattered. But I don't always sleep well. I often toss and turn and awaken at strange hours, and I am not alone. Paradoxically, even as we learn more about sleep, the number of people around the world suffering from sleep problems is rising.
On the continent, South Africa leads the way, with about a third of our citizens reporting some form of sleep difficulty, mostly that they are not getting enough of it.
Dr Ebrahim explains that sleep problems are classified into the insomnias, in which sufferers have difficulty falling or staying asleep; and the less common hypersomnias such as narcolepsy, a disorder in which REM sleep appears during the wrong phase of the sleep cycle, displacing deep sleep and leading to excessive daytime sleeping and drowsiness.
Narcoleptics often have cataplexy too, a bizarre condition in which strong emotions such as anger or surprise cause sudden loss of muscle tone or paralysis.
The parasomnias are another group of disorders, resulting from the complex interactions between consciousness and loss of muscle tone becoming unhinged.
With REM sleep disorder, the normal nocturnal state of paralysis fails to engage and sufferers physically act out their dreams, leaping from windows, climbing bookshelves, or assaulting their bed partners while dreaming that they are under attack. This condition is often a harbinger of neurological diseases such as Parkinson's.
Sleepwalking is a parasomnia that occurs when the parts of the brain controlling movement and spatial awareness remain active, while the centres in charge of consciousness are switched off. During the deep phases of sleep, people who are not dreaming eat, cook, walk, have sex or even drive a car. Although they perform these acts with their eyes open, they have no conscious thoughts or memories of the events.
In 1987 Kenneth Parks, a Canadian man with a history of sleepwalking, drove 20km to his in-laws' house where he assaulted his father-in-law with a wheel spanner and beat and stabbed his mother-in-law to death.
Parks claimed to have woken up in his car with torn, bloody hands and no knowledge of the attack.
He drove directly to a police station and informed the officer on duty that he believed he might have killed somebody. After a lengthy trial he was determined to have been sleepwalking and was acquitted of all charges.
This landmark case spawned the new discipline of sleep forensics, and as more is learnt about the extreme realms of sleep, experts such as Dr Ebrahim are increasingly called to testify at trials.
But the commonest sleep disorder – after insomnia – is caused by simple mechanics. In obstructive sleep apnoea, or OSA, the soft tissues of the throat collapse during sleep, shutting off the airways. After drifting off, sleepers begin snoring and then, as their airways close, they are essentially smothered. Before reaching deep sleep they jolt awake with racing hearts, gasping for air. Exhausted, they fall asleep again and the process repeats itself.
Obesity, alcohol, smoking and nasal congestion exacerbate OSA. The disrupted sleep causes daytime drowsiness, traffic accidents, weight gain, depression and memory problems. Long term, the untreated condition is associated with hypertension, strokes and heart disease.
Dr Shabir Ebrahim, an ear, nose and throat surgeon in Cape Town, (and no relation to Dr Irshaad Ebrahim), shows me the polysomnogram of a young woman complaining of tiredness and snoring at night. She weighs 135kg. Her initial sleep study shows that she jolts awake almost every minute, and that over the course of the night she manages only nine minutes of the expected two hours of REM sleep she needs.
In 1981, an Australian physician named Collin Sullivan attached his vacuum cleaner to a face mask and adapted the device to invent a treatment for obstructive sleep apnoea. The design has since been purpose- built to be less noisy, but the mechanism remains a pump that basically applies positive pressure to keep floppy airways inflated, much like a balloon.
In a follow-up sleep study, with a continuous positive airway pressure mask strapped to her face, the awakenings of Dr Shabir Ebrahim's patient drop dramatically from once a minute to eight per hour. Her REM sleep increases and her daytime drowsiness disappears.
These masks are the gold standard of treatment for obstructive sleep apnoea sufferers but their distinctly unromantic, Darth Vader-like appearance is unappealing, and within a few months only half the devices remain in use, strapped to the faces of those who need them.
For some nose-breathers with moderate OSA, perforated plasters that seal off the nostrils, called "expiratory positive airway pressure" devices, offer an effective and affordable alternative to expensive continuous positive airway pressure machines. Dental plates, weight loss and surgery are other options.
Even for those of us without sleep apnoea or exotic parasomnias, the modern lifestyle with its stress, anxiety, artificial light and electronic devices may wreak havoc on the sleep cycle. However, some sleepers distressed by their inability to maintain unconsciousness through the night, may just be victims of unrealistic expectations.
Research by the American historian Roger Ekrich has revealed that the habit of sleeping in a single eight-hour block is fairly recent. Until 150 years ago we slept quite differently.
"First sleep" took place in the early evening and was followed by a several hours of quiet wakefulness, during which people read, talked, meditated or made love. "Second sleep" then followed.
Anthropologists, after long neglecting the sleep habits of their subjects, then discovered that in traditional societies, from pastoralists to hunter-gatherers such as the San people of the Kalahari, people bed down communally and drift in and out of sleep throughout the night, waking in shifts.
Late-sleeping adolescents and early rising elders ensure that someone is always available to tend the fire and watch for predators. Quiet time at night is spent playing the mbira, talking or thinking.
Among traditional people the most common complaint about sleep was that they were getting too much of it.
In modern society, waking at night often fuels sleep anxiety, the fear of not being able to fall asleep, which results in not being able to sleep, a condition that makes some people reach for the sleeping pills. Accepting the naturally fractured patterns of our sleep cycle could ease that anxiety, as could flexible work hours and a culture that embraces daytime napping.
"It is important to get those seven or eight hours sleep," says Lipinska.
"But it appears that they can be split up within a 24-hour period."
As our knowledge of both normal and aberrant sleep grows, along with insomnia, sleep anxiety, sales of sleeping pills and continuous positive airway pressure machines, it is clear that sleep is vital and strange, and far more important to our physical and mental health than we ever imagined.
Martinique Stilwell is a medical doctor and writer living in Cape Town. Her book Thinking Up a Hurricane was published by Penguin last year
Have something to say? Tweet or Facebook us on @Bhekisisa_MG
Heads of state discussed one of the world's biggest killers in New York this week — and it was Aaron Motsoaledi who got them together.
Interested in health and social justice reporting and willing to put in the hours to do it? This internship might be for you.
When TB strikes, the fight to live can come at the cost of a way of life for the country's nomads. This could help ease the pain.
Bhekisisa means "to scrutinise" in Zulu
In South Africa, Zulu patients who would like to be thoroughly assessed by a doctor, would ask the physician to "bhekisisa" them.