Sleep on it. That’s the advice we’ve all heard when challenged with a seemingly impossible dilemma.

A new study suggests it’s not just folklore. When over 100 volunteers were given the chance to nap, if just for a few minutes, their ability to creatively solve a taxing mathematical problem improved. But there’s a twist. The trick only worked before drifting off into deeper stages of sleep.

In other words, there’s a brief window of creativity, right in the “twilight zone” of sleep as a mind gradually fades into total lack of consciousness.

The study, led by Dr. Delphine Oudiette at Sorbonne Université in Paris, is one of the first to scientifically examine a specific period of sleep—when you’ve just dozed off—that can be tracked by a peculiar brain wave pattern called N1. However, history’s greats, including Albert Einstein, Salvador Dalí, and Thomas Edison, have all purportedly employed a method to tap into that creative “sweet spot,” said Oudiette.

“This study gives us simultaneous insight into consciousness and creativity,” said Dr. Adam Haar Horowitz at the MIT Media Lab, who was not involved in the work.

Edge of Lucidity

Sleep is a multi-step process, gradually descending down the staircase towards unconsciousness. It’s also a cycle, hopping between different sleep states roughly every 90 minutes.

Despite our perception of sleep, the brain is hardly “shut down” during these cycles. One theory suggests that our neural networks sort through previous learnings and physically strengthen connections—or weaken them—to etch important memories into neural circuits. Sleep may also globally dampen the brain’s synapses in an effort to maintain its plasticity—that is, its ability to learn—an idea dubbed SHY (synaptic homeostatic hypothesis), and clear out metabolic waste to protect against Alzheimer’s.

But to dream hackers, perhaps the most intriguing aspect of sleep is our potential ability to learn as the brain is resting. Previous studies suggest that during periods of deep sleep, the unconscious brain can learn new words from a made-up vocabulary, or improve on motor tasks, say, playing music. Sleep’s secret superpower has even galvanized AI to retain its learning, nudging deep learning to absorb and retain or discard information more like the human brain.

Yet as anyone who’s ever kept a dream diary (myself included) knows, it’s terribly difficult to remember dreams from deep sleep. What stick around are experiences in semi-lucidity, a liminal haze where wakefulness blurs into sleep. This stage, dubbed “hypnagogic,” is what intrigued Oudiette.

“Contrary to other sleep stages, the first stage of non-REM sleep has received little attention, and its cognitive role is largely unknown,” the authors wrote. But, they continued, “We believe that N1 presents an ideal cocktail for creativity.”

One-Minute Insight

In this study, the team started with a task and a lie.

They presented participants with a string of eight numbers and provided two rules that could help them guess the next number as quickly as possible. But unbeknownst to the volunteers, the team hid a shortcut to obtain the solution much faster. It’s quite simple: the eighth digit is always the second digit in any sequence. Identifying the pattern would jump-start a participant’s ability to solve the puzzle in record time.

While not artistic creativity, the task taps into a mind’s ability to break away from given instructions to find a novel route towards an answer—the essence of creativity.

To drill into the given two-rule solution, the participants first solved 10 problems using the instructions. People who gained early insight into the hidden shortcut were eliminated from subsequent analysis. A portion of the remaining participants were then asked to briefly shut their eyes and relax for 20 minutes, during which their brain waves, muscle activity, and eye twitches were monitored so the scientists could reliably detect their sleep stage.

Using a technique from Edison, the volunteers held onto an object—a ball or a glass container—that would fall when they entered deeper sleep. Once jolted awake by the sound, they’d record their twilight dream ideas. The goal was to isolate N1 brain wave patterns without contaminating them from other, deeper sleep stages, said the team.

“We tested Edison’s intuition that there is a fleeting, propitious moment for insightful thoughts within the sleep onset period,” the team wrote.

A Hidden Solution

Here’s where it got crazy. After the nap, participants were asked to solve the math problem again. In subsequent interviews, they also described their dreams to the best of their memories.

Remarkably, just one minute into N1 brain waves, the participants had more than an 80 percent chance of utilizing the hidden rule. In contrast, those who stayed awake had less than a 30 percent chance of figuring out the better solution. The team dubbed this the “eureka” moment. But it’s not a one-shot spark of insight. Using the data to train a sleep learning algorithm, the team found that this boost in creative math solving only occurred after on average 94 trials.

Even more surprising was that deep sleep didn’t help. Participants who just dozed off into N1 sleep were nearly six times more capable of solving the puzzle than those who slipped into natural, deep sleep—a brain wave signature called N2. It’s kind of a “spectacular result,” said Oudiette.

The team calls this the “neurophysiology of the sweet spot.” Digging deeper into brain wave signatures, they found that the strength of two particular frequency bands—delta and alpha—could predict insight. Fall asleep too fast—or too shallow—and you’d miss that window.

Overall, the team found that just spending one minute in N1 sleep, the twilight zone, triggered a person to find a hidden rule nearly three times more often than those who were awake but resting. But balance is key. “Retaining it requires a trade-off between the ability to fall asleep and attain N1, but without too much sleep pressure to avoid transitioning into deeper sleep,” they said.

Digging Deeper

Sleep is often considered a bridge between consciousness and intelligence. For Oudiette, the study is personal.

“I’ve always had a lot of hypnagogic experiences, dreamlike experiences that have fascinated me for a long time,” said Oudiette. “I was quite surprised that almost no scientists have studied this period in the last two decades.”

It’s unclear why entering N1 sleep, if just for a few seconds, bolsters creativity. But to Oudiette, it’s possible that the twilight state loosens normal cognitive constraints while retaining awareness, balancing the dream world with reality into an “ideal state.” And because the brain isn’t completely under water, any ideas that result may stick around, allowing us to retain them upon awakening.

For now, the half-sleep highway towards creativity only works demonstratively for this one math task. It’s possible people who napped were simply mentally refreshed, rather than their neural networks reorganizing on a large scale to trigger creativity. To their credit, the authors plan to utilize brain-computer interfaces and further nail down the neural network signatures involved.

But the study’s simplicity is its beauty, said Horowitz.

“It’s the kind of study that you can go ahead and try at home yourself. Grab a metal object, lie down, focus hard on a creative problem, and see what sort of eureka moments you can encounter,” he said.

Image Credit: Mascha Tace /

Shelly Xuelai Fan is a neuroscientist-turned-science writer. She completed her PhD in neuroscience at the University of British Columbia, where she developed novel treatments for neurodegeneration. While studying biological brains, she became fascinated with AI and all things biotech. Following graduation, she moved to UCSF to study blood-based factors that rejuvenate aged brains. She is the ...

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