It may one day be possible to reap some of the benefits of sleep without ever closing our eyes. Stimulating specific brain activity in awake mice led to some of the same effects as deep sleep, including a boost in memory.

“It should be possible, at least in theory and to some extent, to replicate these results in our species,” says at the University of Oxford, who wasn’t involved in the research. “It would be fascinating to explore whether artificially inducing [this activity] during waking [hours] in humans can result in a subjective feeling of being more refreshed and rested afterwards.”

Sleep is thought to be an essential way for the brain to carry out most of its maintenance work. This includes synaptic homeostasis, the process whereby the brain declutters the thousands of new neural connections made during the day – storing important ones and weakening or cutting away ones that aren’t as necessary.

During non-rapid eye movement (NREM) sleep – the deep sleep state that makes up around 80 per cent of sleep in adults – the brain’s cortex repeatedly fires signals at the exact same time and then shuts those neurons off, in a pattern called slow-wave sleep activity. “This has been linked to synaptic homeostasis, and may be a key mechanism underlying sleep’s restorative functions,” says at the University of Wisconsin-Madison.

Cirelli and her colleagues wondered if a small part of the cortex could be nudged into entering this deep sleep state while an individual is still awake. Some animals do this naturally, such as dolphins, ducks and fur seals, in which one half of the brain enters NREM sleep while the other remains alert and vigilant for predators.

To see if a similar state could be induced, the researchers genetically engineered mice so their neuronal activity could be switched off using light. They implanted a probe into one half of their brain and kept the mice awake for five hours by giving them new things to explore. Near the end of this time period, the light probe was repeatedly turned on and off for 30 minutes, mimicking NREM sleep.

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Afterwards, when the mice were allowed to sleep, brain recordings showed that the stimulated side of the brain didn’t show the usual signs of exhaustion caused by sleep deprivation. “Because that small part of the brain did its decluttering while awake, it no longer needed extra deep sleep afterwards,” says Cirelli.

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Next, the researchers wondered whether forcing sleep during wakefulness boosts memory. So they placed the genetically modified mice in a square box with carpet that had the same texture on both sides of the container. After 15 minutes of exploring the space, the mice were assigned to either a sleep group, a group that was sleep-deprived for 1 hour, or a group that was sleep-deprived for 1 hour but received the artificial deep-sleep stimulation.

The next day, the mice went back into the box, but one side of the container had a new texture. Mice are naturally drawn to novelty, so the researchers measured how much they remembered the old environment by the amount of time they spent on the new side. They found that the sleep-deprived mice that received no stimulation seemed to struggle to tell the new and old side apart, while both the sleep group and the sleep-deprived mice that received the stimulation spent more time on the new side.

The team plans to study whether similar effects could come about in people if this brain activity were induced non-invasively via transcranial electrical stimulation. However, Vyazovskiy stresses that sleep can probably never be replaced. “Sleep is of two kinds – NREM and REM [rapid eye movement] – and we still do not know what it is about the alternation of these two states that makes sleep complete,” he says.

Your brain could be gently coaxed into working on complex problems while you sleep, making you better able to tackle them the next day.

Neuroscientists and psychologists are increasingly using sounds, touch, movement and, particularly, smells to influence the content of people’s dreams. This dream engineering has shown promise for , and even .

Now, at Northwestern University in Illinois and her colleagues have shown it could also aid problem-solving. The team recruited 20 self-identified lucid dreamers – people who are aware they are dreaming during a dream and can control the narrative – who attempted a series of puzzles while fully awake across two sessions in a sleep lab. Each puzzle was paired with its own soundtrack, such as birdsong or steel drums.

The researchers monitored the activity of each participant’s brain and eyes to determine when they had entered the rapid eye movement (REM) stage of sleep, when dreams tend to be long and abstract. At this point, the team randomly selected some of the puzzles that the participants had been unable to solve and played their associated soundtracks. The participants were told to indicate lucidity by performing at least two rapid left-to-right eye movements. They also indicated that they had heard the puzzle sound and were working on solving it by doing at least two rapid in-out sniffs.

The next morning, the participants reported being more likely to have the puzzles feature in their dreams if they heard their soundtracks while asleep. What’s more, this increased the chance that they could now solve them: of those who dreamed about the puzzles, about 40 per cent went on to solve them, compared with 17 per cent of those who didn’t report having the puzzles in their dreams.

Although it is unclear why this occurred, pairing the sound stimuli with the learning task while they were awake may have activated memories of that puzzle when they heard the same noise during sleep. Known as targeted memory reactivation, this seems to trick the hippocampus – a brain region that is important for memory – by evoking what looks like a spontaneous reactivation of a memory. This may then influence what the hippocampus replays during sleep, enhancing learning.

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Although dreams can occur at any time during the four stages of sleep, Konkoly thinks the targeting of REM may have enhanced the participants’ problem-solving prowess. “REM dreams are hyper-associative and bizarre. They mix new and old memories together, and even mix memories with fantastical imagination,” she says. “You have this brain that’s active [during this stage], but maybe with less inhibition, so you can reach farther into the corners of your mind.”

at Harvard University says the work shows that “people may be able to deliberately focus on a specific unsolved problem while dreaming”.

But some say dream engineering could disrupt the other functions of sleep, such as clearing the brain of debris, or that it could one day be hijacked by companies taking out advertisements on at-home devices, which Cunningham is particularly concerned about. “Our senses are already assaulted from all directions by ads, emails and work stress during our waking hours, and sleep is currently one of the few breaks we get from that,” he says.

Konkoly now plans to investigate why hearing sound stimuli on different days can have varied results in the same individual. “When running this study, I was up all night, watching people’s brainwaves and cueing them during REM sleep. Sometimes they responded with signals, other times not. Sometimes they woke up and had incorporation of the associated puzzle, sometimes just the sound, and other times nothing. How is it that the same stimuli, presented in the same state of consciousness, can be processed so differently?”