A conscious experience in the midst of sleep, dreams fascinate us as much as they elude us. Research is enabling us to better understand this rich cognitive phenomenon. Delphine Oudiette, a researcher in the DreamTeam at the Paris Brain Institute, and Claudia Picard-Deland, a postdoctoral fellow at the Centre for Advanced Studies in Sleep Medicine at the University of Montreal, shed light on the subject.
Dream nights
A dream is defined as “any mental experience that occurs during sleep” explains Delphine Oudiette. It can range from simple thoughts to the most dreamlike imaginings, depending on the stage and progress of the night. As Claudia Picard-Deland reminds us : “Dreams can be collected from sleepers at any time during the sleep cycle.”
From the moment we fall asleep, we can observe abstract micro-dreams, with the perception of sounds, hallucinatory movements or images, varying from one individual to another. This is one of Delphine Oudiette’s research topics : “One hypothesis is that the different areas of the brain do not all fall asleep at the same rate.” Depending on the mapping of this desynchronisation, we encounter different types of subjective experiences.
As the night progresses, dreams become more complex. “They become more perceptual, more vivid and involve more actions,” explains Claudia Picard-Deland. The sleeper goes through several cycles, each with the following phases : a transition from wakefulness to sleep ; from light sleep to deep sleep to REM sleep. During the light and deep sleep phases, dreams most often take the form of thoughts that stick to reality, but they can be enriched with images. REM sleep is the perfect setting for multisensory dreams, with characters, actions and emotions associated with memories. It can happen that sleepers become aware that they are dreaming without actually waking up : this is called a lucid dream. They are then able to observe their dream or even influence it. This happens more frequently in REM sleep. Finally, in the transition to waking, we find perceptions similar to those of falling asleep.
Unless certain regions of the brain are impaired, it is likely that we all dream, even when we have no memory of them. This is suggested by the observation of patients with REM sleep behaviour disorder (RBD), who externalise their dreams. “Some of them claim never to have had any dreams. Yet we see them in action in their sleep,” says Delphine Oudiette.
What’s the point ?
If dreams visit each and every one of us, they must have some use. So, what benefits do we derive from this dreamlike experience ? “It’s very difficult to differentiate the effect of the dream itself from that of sleep in general, so there are only theories,” says Delphine Oudiette.
One of the best known is that dreams serve as a simulation of threats, allowing us to play out scenarios in complete safety so that we are better equipped in the future. This hypothesis has been tested by examining the dreams of first-year medical students who have passed a stressful competitive examination. The people who had the most negative dreams about the exam were the ones who did best1.
It is also possible that we manage to better regulate our emotions2 thanks to these nocturnal scenarios, in which we integrate the sometimes negative feelings of the day. We would thus relive them in a more neutral, even positive context. The construction of dreams is also a driver of creativity. It combines elements of our life in a strange or abstract way, transforming itself into a source of prolific ideas and inspirations3.
Claudia Picard-Deland emphasises that “the dream is perhaps only a window on certain processes that can take place during sleep,” such as memory consolidation. “It is possible, however, that dreams have a role to play,” she adds, “we still don’t have the means to prove it, but we can find correlations.” She measured better performance in the completion of a task learned the day before among participants who had dreamed about this learning4. She also observed an evolution in the type of memories that are integrated into dreams during sleep. At the beginning of the night, these are recent elements, from the day for example. The further we progress through the sleep cycles, the more distant memories, such as those from childhood, are incorporated into the dreams5. “Dreaming about the day’s learning, creating associations with other memories, would allow them to be integrated,” she suggests.
In touch with dreams
Whatever the theories on the possible functions of dreaming, there is generally little evidence to support them. It should be said that it is difficult to access this intimate experience at the moment it occurs. Some studies are based on the a posteriori reports of dreamers, which makes it possible to target a large number of individuals. However, transcribing a multisensory experience is not easy, especially as the brain likes to reintroduce coherence into the narrative, at the risk of creating false memories6.
“Another protocol, the most common in neuroscience, is that of serial awakenings in the laboratory,” explains Delphine Oudiette. The volunteers are fitted with electrodes to record the stages of sleep (measuring brain activity, muscle tone, eye movements, etc.). Their sleep will be interrupted several times during the night by an interview. The closer it is to the occurrence of the dream, the more likely the account will be accurate.
Some sleep disorders offer real-time windows of observation into the dream. Somnambulism, night terrors, and also RBD can break the muscle barrier that prevents us from moving during sleep7. It is thus possible to observe on video the actions of these patients physically living out their dreams8. However, these nocturnal behaviours are rare, sometimes difficult to interpret, and it is less clear whether the results can be generalised to the general population.
The further we progress through the sleep cycles, the more distant memories, such as those from childhood, are incorporated into the dreams
Lucid dreamers, who have the ability to become aware that they are sleeping, are also involved in the study of dreams. They can communicate from their sleep through pre-established signs, such as eye movements. They thus provide information in real time about their dream9. To maximise the appearance of these windows of consciousness, expert lucid dreamers are called upon, as well as patients with narcolepsy, a sleep disorder, one of the side effects of which is to promote this phenomenon.
Whether reported by narrative or observed in real time, this information about dreams can be correlated with recordings of brain activity to study a dream signature10. Artificial intelligence tools sometimes help to decode this data11.
Towards a better understanding
“The science of dreams means many sleepless nights for the researchers, sometimes with few dreams collected,” emphasises Claudia Picard-Deland, “hence the importance of collaborations and open databases for accumulating recordings.” Like DREAM, it is a collection of dream reports and brain activity recordings collected from around the world12. Lucid dreams are even rarer, and trying to induce them is another way to increase the number of samples. This is another avenue she is exploring.
Gaining a deeper understanding of dreaming also involves improving the quality of the data collected, thanks to more efficient measuring instruments. Ultrasound imaging is full of promise, according to Delphine Oudiette : it would make it possible to record brain activity with a level of precision and signal quality that has not been achieved until now. Currently only used on animals and human babies13, it could soon be used on adults. “It’s quite exciting, this type of technological advance would allow us to make a leap forward,” she enthuses.
“In dream neuroscience, there is everything to be done,” continues Delphine Oudiette. She has recently observed, during certain dreams, windows of connection with the outside world where sleepers are no longer cut off from the world. It is thus possible to communicate with them during their sleep. She is seeking to better understand how this phenomenon works. Does it provide a clue as to how deep sleep is ? Too many of these windows might explain the subjective impression of poor or little sleep in some patients suffering from insomnia. “These people may feel as if they have been awake when they have slept through the night,” confirms Claudia Picard-Deland, who is studying the link between dreaming and insomnia. But her new project concerns a more social aspect : “Telling a dream is revealing oneself to the other, trusting them. Would there be any benefit to sharing it?” For the sake of science at least, telling our dreams will always be of interest.
