Researchers have managed to communicate with people while they were asleep, which could open up new avenues for studying sleeping and dreaming.
In a small study, people occasionally made brief and partial smiles or frowns as they slept in reaction to certain words 鈥� and their responses were usually appropriate. They had no memory of what happened when questioned afterwards.
This is the first time that such communication has been established in those who aren鈥檛 one of a rare group of people who can control their dreams, known as lucid dreamers. 鈥淭hese windows of reactivity could pave the way for real-time communication with sleepers,鈥� says at the Paris Brain Institute in France.
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Oudiette鈥檚 team made the discovery while developing ways to communicate with lucid dreamers, something it showed was possible in 2021. The initial targets were people with narcolepsy, a rare condition in which people suddenly drop off during the day, as they are more prone to lucid dreaming.
But when the researchers asked people who don鈥檛 have narcolepsy and never have lucid dreams to join their study for comparison, they were surprised to find that this group could also sometimes smile or frown in response to cues while they napped, albeit at a lower rate than the lucid dreamers.
The study involved 27 people with narcolepsy and 21 without it. All were asked to listen to recordings, while awake, of someone saying either real words or similar sounds that weren鈥檛 real words. Half of each group were asked to smile, three times, if they heard real words and frown if they heard fake words, while the rest were told to do the opposite.
Next, they were hooked up to electrical sensors on their face to detect muscle movements and sensors on their scalp to record brainwaves via an electroencephalogram (EEG), which can show if someone is awake or in various stages of sleep.
Then the participants were asked to take a daytime nap. The recordings continued to be played intermittently as they fell asleep, with the volume turned down very low.
In the first stage of sleep, called N1, which typically lasts about 5 minutes, the people without narcolepsy gave any response 鈥� whether correct or not 鈥� to the recordings about 20 per cent of the time. In later stages of sleep, the response rate was about 5 per cent, while in the deepest stage they didn鈥檛 respond at all.
The researchers gave the participants some leeway, recording a positive response if the sleeper moved their smiling or frowning muscles twice or more. 鈥淸The task] was hard to perform, even during wakefulness, so we decided to accept any [response] that includes at least two successive contractions of a same muscle,鈥� says Oudiette.
When people did respond, their response was the correct one about 80 per cent of the time.
The overall response rate in those with narcolepsy was higher, ranging from 20 to 65 per cent.
The team now plans to analyse EEG recordings to try to identify any brainwave signatures that indicate when people will respond to hearing sounds, says Oudiette. 鈥淲e could develop tools to detect when these windows will open in real time and then we could send questions right at that moment.鈥�
鈥淚t鈥檚 really nice to see this in non-lucid dreamers,鈥� says at Uppsala University in Sweden. 鈥淚 think it will be a means for us to peer into what鈥檚 going on during sleep.鈥�
Nature Neuroscience
