Your brain may start dreaming before you fall asleep, Parisian study suggests

Dreams can occur during different states of wakefulness, not just during sleep, according to a recent study published in Cell Reports. The study suggests there are actually four distinct mental states during the sleep-wake transition rather than just two – dreaming and waking thought, which may be beneficial to understanding sleep disorders such as paradoxical insomnia.  

Researchers from the Paris Brain Institute, including first author Nicolas Decat, a Ph.D. student there, studied sleep onset in 92 participants using a method inspired by Thomas Edison. The inventor was said to fall asleep holding a heavy object so that when he fell asleep, the object would drop, thus waking him during sleep onset. He would then use the ideas he recalled during this dream-like state and use them to inspire his work.

Participants were fitted with an EEG cap to continuously record brain activity during the study, instructed to sleep and then woken up by using either the Edison-inspired method or an alarm. The moment they woke up, they were asked to describe what they’d just been thinking about.

Researchers cross-referenced patient reports with their EEG results and identified four types of observations, specifically, fleeting recollections such as "I saw an image of my mom" (C1); a high level of connection to the surrounding environment, such as "I was listening to street sounds” (C2); bizarreness, such as "I saw images of small aliens” (C3) and a high level of voluntary control, such as “I was thinking about what I would do tomorrow” (C4), according to the study.

Each of the four states was observed during wakefulness, sleep onset and light sleep.

“Being awake is not synonymous with being attentive, fully aware of one's surroundings, or able to act and think rationally,” Delphine Oudiette, Ph.D.,co-leader of the DreamTeam, the sleep research team at the Paris Brain Institute, said in the news release. “We now know that there is a continuum between wakefulness and sleep, with intermediate states such as mind-wandering or mind-blanking, during which certain regions of the brain may be asleep. What remained to be determined was whether the content of our thoughts also varies independently of our state of vigilance.”

The EEG recorded especially high brain activity during the “bizarre” patterns, considered “the dream-like state.” This was reflected as reduced long-range connectivity between the frontal and occipital regions of the brain and was the state that most closely resembled rapid-eye-movement (REM) sleep dreaming.

The other three categories more closely resembled wakefulness.

C1 appeared as a combination of wakefulness and sleep because of the snapshot-like images seen as one is drifting off to sleep. C2 exhibited brain activity like daydreaming and C4 was more action-oriented, which could be comparable to goal-oriented thinking patterns observed during total wakefulness.

The findings of this study have implications for sleep disorder treatment, specifically when it comes to treating paradoxical insomnia, which occurs when a patient reports they spend hours awake at night, but polysomnographic measurements taken during a sleep study indicate they do sleep. Oudiette explained that a broader definition of sleep and wakefulness may help with treating this type of insomnia.

“Through this lens, some of them may spend an unusually long time in an alert state (C2), hyperconnected to the outside world, or, conversely, very little time in a dream-like state (C3), blurring the line between their waking and sleeping lives,” Oudiette said. “Beyond giving patients' reports the weight they deserve, this approach paves the way to identifying objective markers of insomnia.”