There was also no strong connection between yawning and empathy or intelligence, and age was only able to explain about 8 per cent of variability in the contagious yawn response / Getty Images
We all know that we need it and most of us want more than we get. But no one has ever been able to explain why we sleep, or what makes us dream. Jeremy Laurance visits a new exhibition dedicated to the art and science of shut-eye

Why do we sleep? More than 80 years after the world's first sleep laboratory opened in Los Angeles, and in spite of intensive investigations of the sleeping brain, we still do not know the answer. Sleeping and dreaming remain among the greatest mysteries of the human organism essential to life, yet inexplicable and frustratingly unproductive.

We spend one-third of our lives asleep. Imagine the possibilities if we could do without it. It would be the equivalent of adding 25 or 30 years to the average life-span an enormous gain, at the expense of nothing more than the loss of slumber.

The idea exerts a strong fascination for scientists and lay people alike, and it is investigated in a new exhibition, Sleeping and Dreaming, at the Wellcome Collection, which opens today.

Presented in a dark and dramatically lit space, more than 200 exhibits chart the scientific exploration of sleep, and the social and cultural areas of our lives to which it is linked. They include art works by Goya, Henry Fuseli and Catherine Yass.

While sleep is essential to life, most of us feel we do not get enough of it even those with homes and beds to go to. We are a nation of insomniacs, with two-thirds of the population complaining they cannot sleep. Insomnia is so common that doctors say the preoccupation with it is now itself a medical problem. The greatest enemy of sleep is worry about not getting enough of it. Most people who lose sleep will be able to recover it the next night, and will be able to cope in the meantime.

Prolonged sleeplessness, however, is crippling. Anyone who has gone for two nights without sleep will know what this means the siren call of slumber beckons irresistibly. Peter Tripp, a New York disc jockey, was among the first to discover its cost and he did so in public. He took part in a "wakeathon" in January 1959 to raise funds for polio research, during which he went 201 hours without sleep while continuing to broadcast from a glass booth in Times Square. As the hours passed he became aggressive, started hallucinating and began to suspect his support group of a conspiracy against him. Yet he managed to broadcast for three hours a day throughout, though not without the help of (unidentified) stimulants.

He survived the experiment, and his symptoms of irritation and paranoia became recognised as classically linked to extreme sleep deprivation. But he suffered from personal and professional problems later in his life that would always be blamed on his record-breaking stunt.

Shortly after his "wakeathon", Tripp was indicted in the infamous Payola scandal and found guilty of accepting bribes from record companies for playing their records. He was disgraced, and his career never recovered. He was married and divorced four times and died, aged 73, in 2000. His first wife said he was never the same after the stunt.

And he didn't even keep the record. Five years later, Randy Gardner broke it with a stint of 11 days awake in January 1964. He also experienced hallucinations and became increasingly grumpy with those around him, though he reportedly did without the stimulants. Instead, his friends took him on walks at night and forced him to do press-ups when he showed signs of drowsiness. On completion of his feat, when asked at a press conference how he had done it, he replied: "It's just mind over matter." Then he curled up in bed and slept for 15 hours.

Gardner's record was authenticated by a sleep researcher and professor of psychiatry at the Stanford School of Medicine, on the basis of direct observations and electroencephalogram (EEG) recordings of Gardner's brain. The now-famous professor was named, aptly, William Dement. His letter is part of this display at the Wellcome Collection.

While Tripp and Gardner tested the outer limits of sleeplessness, its damaging effects are felt far sooner and can sometimes be catastrophic. In one corner of the exhibition are displayed a few greasy pebbles and two test tubes containing a couple of young, malformed salmon the legacy of the Exxon Valdez disaster in Alaska. When the tanker ran aground on 24 March 1989 and discharged 260,000 barrels of crude oil into the sea, it triggered one of the worst ecological disasters in history, which cost an estimated $2bn to clear up. The official inquiry by the National Transportation Safety Board concluded that overtiredness of the crew was a key cause.

Lack of sleep has similarly been blamed for the Chernobyl nuclear reactor disaster in what is now Ukraine, the Three Mile Island nuclear reactor breakdown in the US, and the Challenger space shuttle accident that claimed the lives of its seven astronauts.

At a more mundane but no less important level, tiredness is known to be a key cause of motorway accidents. Scientific films made of subjects driving a simulator show the terrifying consequences of sleep deprivation. As their blinking speeds up and their eyes start to close, the vehicles they are nominally in charge of slew across the carriageways, ending up, in one case, in the middle of a field.

The experiments, conducted by the Technological University in Berlin in association with Volkswagen, are part of research towards the development of an infra-red detector that could be fitted in cars and would sound an alarm when rapid blinking began and the eyes started to close.

Even these virtual motorway accidents are not as disturbing as the story of Michael Corke, a music teacher in Chicago, who died of sleeplessness in 1993. A grainy amateur video shows him at his last school concert, walking unsteadily to the conductor's podium and raising his baton, as if he were 90 years old. At that point, he had gone two months without sleep.

Soon after, he was admitted to the University of Chicago hospital. Doctors initially diagnosed multiple sclerosis. Pictures from the Wellcome exhibition show him in his hospital bed, barely able to speak, after 130 days without sleep. Doctors administered sedatives in a dose sufficient to induce coma in any normal human being, but Corke was unaffected. He was finally diagnosed with the rare genetic disorder of fatal familial insomnia, for which there is no treatment and no cure. He died, aged 42, after six months without sleep. The condition has so far been identified in just 25 families worldwide.

Efforts to understand the causes and role of sleep begin with Aristotle, the first person to consider sleep in a methodical way. His treatise "On sleep and sleeplessness" argued that it was caused by the heart cooling down. Other Greek philosophers and physicians said its cause lay in the isolation of the body from its senses but they took the brain rather than the heart to be the centre of the body's sensory perception.

Not until 2,000 years later did it become possible to study the sleeping brain directly. Nathaniel Kleitman opened the first sleep laboratory at the University of Los Angeles in 1925. His team were the first to discover that sleep consisted of different stages, with REM (rapid eye movement) sleep alternating with deeper sleep every 90 minutes. Kleitman's work laid the foundation for modern sleep research.

Dreaming, which occurs during REM sleep, is the one event during the hours of slumber that turns out to be more productive than it appears. Paul McCartney claimed to have woken from a dream with the theme for The Beatles' hit "Yesterday" in his head. Robert Louis Stevenson said the story of Dr Jekyll and Mr Hyde came to him while asleep, and Dmitri Mendeleev reported that he "saw" a chart of all the elements ranged in front of him while dozing at his desk on 17 February 1869. Two weeks later, he published what has become the Periodic Table of the Elements.

Claims such as these allowed entrepreneurial firms in the 1960s to exploit a credulous public by selling the idea of learning in our sleep. Languages were popular simply place the tape recorder by your bed and wake up speaking French.

Freud made the first serious attempt to penetrate the world of sleep with his most famous work, The Interpretation of Dreams, published in 1899. Among his best-known cases was that of the Wolf Man, a rich young Russian called Sergei Pankejeff who had a nervous breakdown at the age of 17 that left him incapable of leading a normal life. His therapy focused on a nightmare he had at the age of four, when he dreamed that he opened a window to see half a dozen wolves sitting motionless in a tree. Freud concluded that this reflected a "primal scene", witnessed by Pankejeff, of his parents having sex.

Although the account strikes a modern audience as dated and contrived, Freud's theory that the "manifest content" of a dream (what appears to the dreamer) is created by the unconscious desires that give rise to it has stood the test of time. By analysing the manifest content, Freud claimed it was possible to trace the desires underlying the dream that were too painful or distressing for the dreamer to acknowledge directly. Dreams became the "royal road to the unconscious".

It is fashionable to dismiss Freud's theories today as misguided. But, in an essay in the exhib-ition catalogue, Professor Mark Solms, a neurosurgeon at St Bartholomew's and the Royal London School of Medicine, writes that research over the last 100 years confirms Freud's view.

"The current neuroscientific evidence gives every reason to take seriously the radical hypothesis first set out in Freud's book that dreams are motivated phenomena driven by our wishes... In fact, aspects of Freud's account of the dreaming mind are so consistent with the currently available neuroscientific data that I personally think we would be well advised to use Freud's model as a guide for the next phase of our neuroscientific investigations."

Just where this leads will depend as much on the needs of a global economy as on the desires of its citizens. The modern 24-hour society, with its round-the-clock provision of services, has radically changed our sleep habits. Instead of our biological clocks, the sleep of modern workers is regulated by alarm clocks, electric light and artificial stimulants.

Power napping is an essential tool for top executives, especially in Japan, where inemuri, as it's called, is widely practised and accepted as a sign of hard work. The powerful, like the powerless, doze when they can. Regular adequate sleep six to eight hours, in a comfy bed has become a luxury for many, something of which they can only dream.

Sleeping and Dreaming, Wellcome Collection, Euston Road, London NW1, to 10 March 2008, entry free (020-7611 2222;

Sinking feeling? How art has opened door to land of dreams

"We are such stuff/As dreams are made on; and our little life/Is rounded with a sleep," says Prospero in The Tempest. Sleep and dreams feature heavily in Shakespeare. "To sleep: perchance to dream ay, there's the rub. For in that sleep what dreams may come?" ponders an anguished Hamlet while wrestling with his dead father's advice. Slumber is suggested in the very title of A Midsummer Night's Dream, wherein Titania, the Queen of the Fairies, awakes from her sleep only to fall in love with the grotesque Bottom.

Artists have long been influenced and inspired by their nocturnal muses, and many of their fantastical works form the basis of the Wellcome Collection's new show. In a sequence of etchings by Francisco Goya, Los Caprichos, the artist depicts a terrifying world of night and dreams, which explore the darkest side of human nature. In El sueno de la razon produce monstruos (The sleep of reason brings forth monsters 1797/ 1798), he shows a poet, asleep over his manuscript, while owls and bats, and other fantastical creatures of the night, rise above his drooped head.

Johann Heinrich Fssli's painting The Nightmare was one of the most famous paintings of the late 18th century, and an engraving of it, by Martin Johann Schmidt, also hangs in the Wellcome exhibition. In it, an incubus squats over a sleeping woman, while a horse peeps through curtains. The work is lent an even greater menace when you realise that the horse is supposedly symbolic of unfettered sexual desire.

But it was only after the publication of Sigmund Freud's The Interpretation of Dreams in 1899 that the study of sleep and dreams really began to seize the imagination of artists. Freud's work was a huge influence on the surrealists, and particularly Salvador Dali and Luis Buñuel, who were so inspired by the psychoanalyst that together they made Un Chien Andalou in 1929. In the film's central somnambulant sequence a man with a razor slits a woman's eye and ants emerge from a hole in a man's hand, both suggesting Freudian free association. Elsewhere in the Wellcome show, Sergei Pankejeff, one of Freud's patients, depicts his interpretation of a dream in which white wolves are seen sitting in a tree. His vision, Freud concluded, represented the "primal scene" of his parents having sexual intercourse.

Contemporary artists are also represented here, including Catherine Yass, whose photographic portraits try to capture the essence of dreams, and Rodney Graham, who took a strong sleeping tablet for a film in which he remembers the comfort of being asleep at night in the back of his parents' car as a child.

Sleep is a source of inspiration for music, too. In one room of the exhibition, "Yesterday" plays, recalling how the song came to Paul McCartney in a dream.

Ciar Byrne

* Most adults need seven or eight hours' sleep a night

* Margaret Thatcher, Napoleon and Florence Nightingale only needed four

* A cat sleeps for an average of 12 hours a day

* Most of our dreams occur during rapid-eye movement (REM) sleep. We have around three to five REM episodes a night

* About 2,500 people in the UK suffer from narcolepsy a condition that causes them repeatedly to fall asleep in the middle of a meal, at the wheel of a car or in mid-conversation

* An adult sleeping for eight hours will burn approximately 50 calories

* A giraffe sleeps for an average of 1.9 hours a day

* Almost two thirds of the population claim they do not get enough sleep