Almost a century ago, an eccentric English lady found the secrets of dream control. Her subsequent adventures explored the limits of consciousness – and modern scientists are only just catching up.

As with many nightmares, Mary Arnold-Forster was being chased. She seemed to be in London around the First World War, and she had somehow become embroiled in dangerous espionage.

“I had succeeded in tracing the existence of a complicated and dangerous plot against our country,” she noted in her diary. “The conspirators had turned upon me on discovering how much I knew.” Eventually she found shelter, but they were closing in. “The arch-conspirator, a white-faced man in a bowler hat, had tracked me down to the building where I was concealed, and which by this time was surrounded.”

At which point, many of us might have woken up in a cold sweat. But Arnold-Forster was made of steelier stuff. She had discovered a method of “dream control”, meaning that she was perfectly aware that she was asleep, and that everything around her – the pursuer, his bowler hat, the very ground she was standing on – was simply a figment of her mind.

So rather than flee, she decided to immerse herself in the thrill of the chase. “All fear had departed; the comfortable feeling of great heroism, only fully enjoyed by those who feel themselves to be safe, was mine.” The night terror had morphed into “a delightful dream of adventure” – allowing her to fulfil her fantasies of subterfuge and espionage from the comfort of her bed.

Inspired by her success, she soon used her nocturnal adventures to touch on some of the greatest mysteries of our slumbers

Lucid dreaming is now well known, but at the turn of the last century, few had explored its potential. Inspired by her success, Arnold-Forster soon used her nocturnal adventures to touch on some of the greatest mysteries of our slumbers. What happens to the mind in the strange “twilight zone” between waking and sleep? Where do the images of our dreams come from? And why do memories of dreams evaporate like the morning mist?

The result is a detailed “traveller’s guide” to the dreamscape – charting the outer boundaries of consciousness as they had never been explored before. Her findings were at odds with almost everything written at the time – yet history has proven that many her theories were spot on. Even 100 years later, scientists are still finding themselves inspired by this unknown pioneer. You too may find some useful tips for ways to spice up your own dreams.

Arnold-Forster was born in 1861 into the English aristocracy. Her husband was the politician Hugh Oakeley Arnold-Forster, the nephew of the celebrated author EM Forster of A Room with a View and A Passage to India fame. She may have remained a mere footnote in the lives of these powerful men, had she not, at the age of 60, published a little-known book named Studies in Dreams.

She does not say exactly when explorations began, but her interest seems to have taken a more serious turn during World War I, when she was haunted by dreams about the deaths of her sons on the front.

The solution, she found, was to repeat a kind of mantra through the day and just before sleep: “This is only a dream; if you wake, it will be over, and all will be well again.” As she had hoped, the incantation made its way into the dreams – so that she would realise she was in the middle of a fantasy. Soon, visions of the dreaded telegrams no longer haunted her nights. “It would be difficult to express how great was the relief when I knew that I could lie down to sleep free from this particular dread,” she wrote.

Once she was aware of her dreams’ true nature, she could instead immerse herself in the fantasy and revel in the daredevil adventures

In gaining this consciousness while asleep, she had discovered a method: lucid dreaming. (Indeed, a repetitive mantra, also known as “auto-suggestion”, before sleep is now considered one of the best ways of achieving a lucid dream.) And like many lucid dreamers after her, Arnold-Forster soon realised that she didn’t have to wake up from a bad dream to avoid the terrors; once she was aware of her dreams’ true nature, she could instead immerse herself in the fantasy and revel in the daredevil adventures.

She was particularly keen to test out the limits of the body in the dreamscape – and her abilities to fly. “By giving a slight push or spring with my feet I leave the ground,” she wrote. “A slight paddling motion by my hands increases the pace of the flight, and is used either to enable me to reach a greater height, or else for the purpose of steering, especially through any narrow place, such as through a doorway or window.” In her dreams, she would even clothe herself in a “flying skirt” that modestly covered her feet as she hovered over the ground.

After I had thought long about flying over trees and buildings, I found that I was getting the power to rise to these heights with ever-lessening difficulty

Surprisingly, the skill required dedicated practice; apparently, even in dreams, we cannot achieve great feats without a little effort. “It was a long time before I could fly higher than five or six feet from the ground, and it was only after watching and thinking about the flight of birds, the soaring of the larks above the Wiltshire Downs, the hovering of a kestrel, the action of the rooks' strong wings, and the glancing flights of swallows, that I began to achieve in my dreams some of the same bird-like flights. After I had thought long and often about flying over high trees and buildings, I found that I was getting the power to rise to these heights with ever-lessening difficulty and effort.” Eventually, she tested her dream skills by attempting a long dream flight across the Atlantic.

Decades later, such colourful accounts would catch the attention of Allan Hobson, now a professor at Harvard Medical School, who was told about the book at a party. In between stints at his hospital’s schizophrenia unit, he tried to put her tips into practice.

I could fly. I could make love to whomever I pleased. I could even wake myself up, the better to recall my exotic dream adventures

“Sure enough, I was soon dreaming and aware that I was dreaming; I was lucid. I could observe and even direct my dreams,” he recently wrote of the experience. “Also, like Mary Arnold-Forster, I could fly. I could make love to whomever I pleased... I could even wake myself up, the better to recall my exotic dream adventures, and then go right back to the same or some more preferable dream behaviour. This experience helped to convince me that dream science was not only possible but extremely promising.”

Along with Ursula Voss at the Goethe University in Frankfurt, Hobson has now scanned the brains of lucid dreamers to try to understand how the dreaming brain – normally passive – wakes up with the heightened self-awareness and agency that characterises lucidity. It is akin, they say, to the moment in human history when we rose from the basic perceptions of animals to the thinking, feeling, self-aware creatures we are today. So far, they think it can be pinned down to a few correlates – high activity in the frontal lobes and a certain breed of “gamma” brain waves. If so, that may be the signature of our higher state of consciousness.

Others are reinvestigating lucid dreaming as a cure for nightmares – just as Arnold-Forster had suggested – particularly in children.

Looking carefully at Arnold-Forster’s accounts, it is not hard to find many other ways in which she pre-empted modern theories of dreaming. For all the whimsy of her stories, she was entirely serious about her attempts to chart the unexplored corners of the sleeping mind. “Our task as students of dreams should therefore be to find out by experiment and careful observation all that we can learn about the working of the various mental faculties in the dream state,” she wrote.

The awakening of lucidity is akin to the moment in human history, when we rose from the basic perceptions of animals to the thinking, feeling, self-aware creatures we are today

Consider dream symbolism. Sigmund Freud’s The Interpretation of Dreams had been published two decades before Arnold-Forster’s Studies in Dreams, and his theories of psychoanalysis were already shocking and fascinating Europe’s fashionable intelligentsia. Yet Arnold-Forster mostly rejected his theories that dreams were allegories of our basest impulses. “My experience convinces me that it is not true that all dreams are symbolic,” she said. “Happily there is no need for us to believe that the nature of the dreams, which for so many of us make up so great an element of pleasure in life, has any close relationship with the morbid obsessions of disease.”

Instead, she pointed out that our dreams are built from a far more mundane substance: our memories. “It happens constantly that some idea that fills our thoughts on one day will determine the course of our dreams either on the following night or after an interval, a few nights later.”

As we sleep, the brain rifles through our experience to index them and pass them over to long-term storage

Today, all of this can be explained by our knowledge of memory consolidation.  As we sleep, the brain rifles through our experience to index them and pass them over to long-term storage. In doing so, it may reactivate the circuits involved in the memory, so they enter our dreams in surprising and sometimes surreal ways. Crucially, Arnold-Forster’s estimate of the timings were impressively accurate  – memories first enter our dreams around one to two days after an event, and then a week later, leading to a so-called “dream-lag effect”. This could reflect the fact that the brain cements its memories in two distinct stages.

Unlike her contemporaries, Arnold also saw the close parallels to the free association we might enjoy when our mind wanders during the day. “The elaborate process of dream building is very much like the process that is carried on in the mind by day when images pass quickly across it, and one association calls up another,” she wrote. “Only at night the imagination is not fettered by the discipline which restrains our wandering thoughts from following too eagerly in the random track of every chance thought and suggestion.”

Scientists now believe that this reflects the brain’s “default network” – an interconnected web of brain regions that can walk through different memories and ideas. This state of free association is, in fact, thought to fuel our waking creativity. The difference is that when we sleep, our frontal cortices – which deal with logic and attention – are even less active, leading one paper conclude that “dreaming can be understood as an ‘intensified’ version of waking mind wandering”. In doing so, they perfectly explain how the brain becomes “unfettered” from the “discipline” of our waking logic, as Arnold-Forster so elegantly described.

The diffuse brain activity may explain why dreams often vanish when we wake, as the morning mist vanishes in sunlight

The slow activation of the default network may also lead to the strange “hypnagogic images” that flash before our eyes in the twilight zone between waking and sleeping – an experience that Arnold-Forster poetically details in her chapters on the “borderland state”. Conversely, when we wake, the diffuse brain activity may explain why dreams often fail to stick in our minds the following morning, why they “they vanish when we wake as mist vanishes in sunlight”, as Arnold Forster put it. Her solution was to allow the dream “to unroll itself very quietly backwards in a series of slowly moving pictures” – until you have slowly pieced together its whole story.

As more and more scientists continue the work started by this eccentric, aristocratic pioneer, her ideas may prove to be only the start of a much greater understanding of the sleeping mind. Arnold-Forster admitted there were many more mysteries to explore, but she would no doubt have been surprised by the new interest in her “little book”, as she modestly called it. Her primary aim, she said, was simply to help us all appreciate the sleeping mind a little more – “to remind us of the measure, too often overlooked, that is added by our dreams to the sum of life's happiness”.

After all, we spend a third of our lives asleep – yet few of us take much notice of those nightly escapades.  “It is only when dreams of terror, dreams of grief, and dreams of evil have ceased to have power over us that we are able thoroughly to enjoy our dream life,” Arnold-Forster wrote. “For it is only then that we are able to embark with entire confidence on the nightly adventure of our dreams, and to explore the unknown and delightful country to which they lend us the key.” If we follow her lead, that delightful country may now be open to us all.

David Robson is BBC Future’s feature writer. He is @d_a_robson on Twitter.

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