The mysterious mechanics of dreams



JI am at the edge of a pond. The ground is muddy, the water dirty and shallow. All around, a myriad of yellow baby bird beaks open to call for food. I approach one of the beaks: it is in fact… an oyster! “, says Clara, 21. The young woman is fond of these accounts of incongruous, funny or fanciful dreams, which she compiles on her Instagram page “I dreamed that”. But what happens in his brain to go from rooster to donkey, or rather from beak to oyster?

Once asleep, Clara goes through different phases. First, a slow sleep: the brain waves slow down, fleeting images or thoughts pass by. Nothing very substantial. Then comes REM sleep: brain activity accelerates, almost similar to waking. Under the eyelids, the eyes start to move quickly, as if watching an animated scene. The dreams are then more vivid, with more successful scenarios. And at the same time, the body is paralyzed: this muscle lock prevents us from carrying out the gestures that we do in dreams.

In the 1950s, the discovery of this paradoxical sleep shifted the study of dreams into the scientific field: until then approached only through the psychoanalytic prism, with the idea of ​​an interpretation to be extracted. (read next page), dreaming is now seen as a cognitive activity in its own right. Interesting to study to explain how and why we dream, but also to better understand the usefulness of sleep, the emergence of consciousness, even to better treat certain diseases.

However, in recent years, the development of neuroimaging techniques has given new life to the neuroscience of dreams. Francesca Siclari, neurologist and researcher at the Center hospitalier universitaire vaudois (CHUV) in Lausanne (Switzerland), thus uses high-density electroencephalography: a helmet equipped with more than 250 electrodes which allows the electrical activity of neurons to be recorded.

During the dream, “We see that certain posterior zones are particularly active, those which generate sensations and visual images”, explains the Swiss researcher. “This ‘hot zone’ located at the back of the brain would therefore be like a screen where the images of dreams appear. By observing it, we were able to tell whether the subject was dreaming or not with 87% accuracy. “

A team of Japanese researchers went further, in 2013, by decoding the content of the dreams of three patients when they fell asleep. They were able to guess – with relative accuracy, 50-70% – whether the sleepers had dreamed of a person, a piece of furniture or a book, thanks to brain imaging. A first (small) step towards a dream-reading machine? “Conceptually it should be possible in the not too distant future, but technically it remains a challenge, it would be necessary to train computers with a lot of dream stories”, explains Francesca Siclari.

“All the same, this work marked a major breakthrough, analysis Delphine Oudiette, researcher at Inserm. They gave their credentials to the dream study, taking advantage of the latest advances in neuroscience. ” Problem: since then, no study has been able to confirm these results. They therefore remain to be handled with precaution, warns Perrine Ruby, from the Lyon Neuroscience Research Center (1): “We have not yet identified a reliable neurophysiological correlate of dreams. Our only access remains the dream report, which is made a posteriori, during waking and which is potentially biased. “

And this is the real challenge of this stammering field of research, subject to an elusive subject. The rigorous analysis of dream accounts collected in the laboratory and stored in “dream banks” – such as, at the University of Santa Cruz, DreamBank, which has more than 22,000 – however, allows us to learn more about them. characteristics of dreams. Sweeping away some received ideas.

“Dreams occur mostly in mundane places, with familiar characters and revolve around activities engaged in waking life”, details on his website Antonio Zadra, researcher in sleep medicine at the University of Montreal. As for typical dreams, like losing teeth, falling into the void or flying, “They represent only 1% of our dreams”, notes Delphine Oudiette. We remember them because their oddity marks us: we are more inclined to tell about our nocturnal flight over Kilimanjaro than a banal dream of scrabble at Grandma’s.

In fact, most of our dreams have a negative tone. They have a great emotional charge and a multisensory dimension that makes them very realistic. “A sensation perceived in a dream activates the same areas of the brain as when it is experienced when awake, details Francesca Siclari, in Lausanne. From a neurological point of view, dreams are therefore hallucinations: perceptions of things that do not exist, only in our head. And are also delusional, because we take this experience for reality. “

However, some dreamers manage to realize that they are dreaming, and can sometimes even act knowingly on the scenario of their dream: we then speak of lucid dreams. A valuable window of access for neuroscientists. A study published in February 2021 in Current Biology even shows that it is possible to dialogue in real time with lucid dreamers, thanks to an eye code or facial contractions (read The cross March 23). Opening new paths in the study of consciousness.

At the Pitié-Salpêtrière Brain Institute, Isabelle Arnulf is interested in patients with behavioral disorders in REM sleep, who have very agitated dreams, experienced with words and actions. However, recognizing these agitated nightmares would make it possible to better anticipate and monitor Parkinson’s disease. New track to explore … “We are really in the infancy of research on the dream, concludes Delphine Oudiette, at Inserm. Everything remains to be discovered… Today we know more about how the stars work than about us! “

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