Sleep is normally thought of as a state in which the body and mind are at rest, disconnected from the rest of the world, so to speak. But the boundary between being awake and asleep is much blurrier than it seems, French researchers write a new study.
They show that normal people can pick up verbal information that comes to them through a human voice in their sleep. They may even respond to this by tensing their facial muscles in different ways. This fascinating property arises occasionally during each sleep phase, like a kind of connection hatch with the outside world that opens at regular intervals.
1001 forms of consciousness
It may make it possible to develop standard communication protocols with sleeping people, to get a better idea of how mental activity changes during sleep. Communicating with people during sleep can make it easier to understand the cognitive processes that underlie normal and disturbed sleep patterns.
“Sleep is an extremely complex phenomenon, even though it seems very simple and ordinary, because we fall asleep every night,” says neuroscientist Lionel Naccache. “Our research shows that wakefulness and sleep are not stable states. On the contrary, we can describe them as a mosaic of conscious and unconscious moments.”
Sleep disorders due to balance disturbance
In order to improve people’s sleep, it is crucial to find out how the brain works in waking and sleeping states. “If we are out of balance, this can cause disorders such as sleepwalking, sleep paralysis, hallucinations, the feeling of not having slept all night or just sleeping with our eyes open,” says sleep researcher Isabelle Arnulf.
To distinguish between wakefulness and the different sleep phases, researchers usually use physiological indicators such as specific brain waves that can be seen on an EEG (electroencephalogram). Unfortunately, these brain films do not provide a detailed picture of what exactly is happening in the head of a sleeping person. Sometimes they even contradict a test subject’s testimonies. “We need more accurate measuring instruments that confirm the experience of a sleeping person. This way we can better estimate the level of alertness,” says researcher Delphine Oudiette.
Narcolepsy and REM sleep
The French team therefore examined 22 people without sleep problems and 27 narcolepsy patients, or people who regularly fall asleep uncontrollably during the day. People who suffer from narcolepsy often have lucid dreams, where they realize they are asleep. Sometimes they can even direct their dreams and completely shape their own dream scenario. During the day, they can easily and quickly enter the braking phase of sleep – the sleep phase in which lucid dreams occur.
The scientists selected narcolepsy patients to investigate the level of consciousness during sleep under experimental conditions. “One of our previous studies already showed that during lucid REM sleep it is possible to communicate with dreamers and vice versa. Now we want to know whether this is also possible during other sleep phases and in people who do not lucid dream,” says Oudiette.
Lucid dreaming with a smile and a frown
The participants took a nap in the lab, after which they were given a word choice test consisting of real and non-existent spoken words. The subjects had to group the terms in their sleep by producing a smile or frown. Meanwhile, their brain and heart activity, eye movements and muscle tension were measured. After waking up, participants had to report whether they had lucid dreamed and whether they remembered anything from the interaction.
“Most participants responded well to verbal stimuli during sleep, whether they were narcoleptic or not. This turned out to happen much more often during lucid dreaming, where there is a much higher level of consciousness. But we also saw communication to a lesser extent in all other sleep phases, both in normal sleepers and in narcolepsy patients,” Arnulf explains.
Acceleration of brain activity
By combining all data, it appears possible to predict the opening of these connecting hatches. When these ‘shutters were open’, the subjects could answer the question whether a word was real or made up. There was a clear acceleration of brain activity and other physical responses linked to high cognitive activity. “In the lucid dreamers, the ability to respond to words was linked to a specific electrophysiological pattern,” Naccache explains.
More research is needed to find out whether the frequency of these reaction periods says something about sleep quality and whether these moments can be used for learning or to cure certain sleep disorders. “The use of advanced neuroimaging techniques will hopefully give us a better picture of the brain mechanisms responsible for sleep behavior in the future,” concludes Oudiette.
It seems that sleep is a much more active and conscious state of being than we have always thought, with the sleeper at times clearly open to the world and people around him.
2023-10-15 17:02:17
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