Every night, our mind embarks on a journey for six to eight hours, and we often bring back only crumbs upon waking. Why do we dream? Where do these images come from? Do blind people see in their dreams, and do sleepwalkers dream? Long reserved for dream interpreters, dreaming has become a true subject of study, observed in sleep laboratories with sensors, infrared cameras, and thousands of accounts. What has been learned there is often more surprising than any dream interpretation key. Decoding.
Why do we dream? Serious leads from science.
Why do we dream? Science does not yet have a single answer, but it offers several serious leads: dreaming may help consolidate memory, soothe emotions experienced during the day, and train for danger.
The memory hypothesis is based on very concrete experiments. In rats, certain neurons in the hippocampus (the "place cells") replay the path of a maze learned during the day while sleeping. Block them at night, and the animal forgets everything by the next morning. Does the rat dream of its maze? Impossible to know...
The danger hypothesis starts from a simple observation: 70 to 80% of our dreams have negative content. For Finnish psychologist Antti Revonsuo, these scenarios of falling or being attacked serve as virtual training, much like a sleeping cat that hunts, fights, and keeps watch in its sleep. A compelling theory that still needs confirmation.
The last, bolder hypothesis: REM sleep, the phase of the richest dreams, begins in the fetus before any other type of sleep. It then occupies a huge place in newborns and could therefore provide the brain with innate behavior programs, a sort of testing ground long before the child knows how to use them.
Paradoxical sleep or slow sleep: the moments of the night when we dream.
We primarily dream during REM sleep, a phase that occurs approximately every 90 minutes, during which the brain becomes active almost as if it were daytime while the body remains paralyzed. However, we also dream, albeit briefly, during slow-wave sleep and at the moment of falling asleep.
REM sleep was discovered by chance in 1953 by a technician in a sleep laboratory who was watching his child sleep and noticed their eyes moving rapidly under their eyelids. This phase accounts for 17 to 23% of our sleep time. In 1962, French neurobiologist Michel Jouvet named it "REM sleep": the brain is very active while the muscles are completely relaxed.
The numbers speak for themselves. When awakened after 10 minutes of REM sleep, 97% of young people and 81% of those in their sixties report having had a dream. During slow-wave sleep, 54% still report dreams (from 1954 to 1966, researchers believed that dreaming only occurred during REM sleep!). Dreams during slow-wave sleep are simply shorter: beyond 40 words, all narratives come from REM sleep.
And what do our eyes look at? They can move at 58 degrees per second under the eyelids. In patients who mimic their dreams, just over half of the scenes are accompanied by eye movements, and the gaze then moves in the direction of the action.
As for falling asleep, it's the moment when images appear before our eyes. You may also be familiar with that feeling of missing a step that makes you jump...
Why We Don't Remember Our Dreams (and How to Remember Them)
We forget most of our dreams because a dream is much easier to remember when we wake up during the night. Great dreamers do not sleep differently than others: on average, they simply wake up more often.
An ordinary sleeper remembers two dreams per week, but the variations are enormous: less than 0.4% of people recall no dreams throughout their lives, while others recount five to ten per night!
Memory peaks in adolescence and then declines with age, and women remember their dreams more often than men. Among great dreamers, the area of the brain that pays attention to what we do and feel is said to be more active.
The good news is that dream memory can be trained:
Keep a notebook or your smartphone by the bed and write down your dream as soon as you wake up (or dictate it to a voice recorder).Also note every nighttime awakening: these are prime moments to capture a dream.Keep this journal for at least two weeks, allowing your memories to become regular. The more interested you are in your dreams, the more the pages will fill up!Be wary of memorable dreams: nightmares and strange dreams stick in memory better than others and give a distorted idea of our nights.
Where do the images of our dreams come from?
The images of our dreams primarily come from our own lives: more than 65% of dreamed events directly relate to experiences from the previous days. However, dreams almost never replicate reality; they reconstruct it in their own way.
A scene from the day is replayed as is only in 2% of cases. The rest draws from our ordinary concerns (family, loved ones, leisure, studies, or work) and recomposes them differently. The journal of a man who recorded his dreams for years illustrates this well: his partner appeared in 3 to 9% of his dreams when they lived apart, compared to 16 to 23% when they were together.
In terms of sensations, sight overwhelmingly dominates, and sounds are present in just over half of dreams, while taste, smell, and touch feature in less than 1% of accounts. As for emotions, fear and anger clearly outweigh positive emotions: this is shown by a database of 50,000 dreams collected from over 500 people.
And what about the so-called "typical" dreams? More than 75% of people have dreamed that they were losing their teeth, yet this dream accounts for less than 0.05% of systematically collected accounts. The same goes for flying: 30 to 63% of people have flown in dreams, but unassisted flying appears in only 1.2% of studied dreams. They leave such a strong impression precisely because they are rare...
Another curiosity: we read very little in dreams (7% of dreamed activities, compared to 23% of our waking hours).
Do blind people dream in images?
Blind people dream in images when their blindness occurs after the age of 5: they still see images in dreams throughout their lives, even if these images fade and become rarer over the years. For those blind from birth, the answer is more surprising: some seem to "see" in dreams, but not in the way a sighted person does.
Left to their own devices, blind dreamers recount dreams filled with sounds, smells, tastes, touches, and emotions, with many movements... often complicated ones.
For a long time, researchers believed that blind individuals used the verb "to see" figuratively. A Portuguese experiment changed the game: ten blind participants and ten sighted ones slept in a lab and were awakened every 90 minutes to recount their dreams. When a blind person's narrative contained images, the electroencephalogram showed a change in activity at the back of the brain, in the visual areas.
How is this possible? When a blind person reads Braille with their fingertips, their visual areas light up as well, because their brain has reorganized itself to "see" through touch. These same regions could therefore be activated during the night.
A revealing detail: when asked to draw their dream, one participant depicted the sun as a disk with two eyes and well-separated rays. Exactly how children are taught to draw it! Perhaps a memory of a raised drawing touched one day, rather than an image seen.
Deaf, paraplegic, amputee: in dreams, the body is whole.
In dreams, most disabled people are no longer disabled: those who are deaf from birth hear and speak, paraplegics walk, and amputees regain the use of their limbs. The dreamer exists in a virtual body, but one that is whole.
A German team verified this with individuals who have been deaf and mute since birth. Mixed with those of hearing students, their dream narratives could never be identified by the evaluators. Nearly half of these dreamers (49%) reported hearing speech in their dreams, and 43% spoke themselves, effortlessly and almost telepathically. One participant even dreamed that she heard a stranger answer the phone in English... and that she understood everything.
Paraplegics, on the other hand, walk in dreams, and even more often than able-bodied individuals: 38% of their dreams feature the voluntary use of legs, compared to 28% among able-bodied people. Those who have never walked in their lives walk in more than 44% of their narratives. A former soldier from the Liberation of Paris, paralyzed since 1944, still walked in his dreams at the age of 85.
The Freudian explanation of hidden desire doesn't really hold here (for a paraplegic, the desire to walk is anything but hidden!). Another avenue involves mirror neurons, which activate when we watch someone act as if we were performing the action ourselves: by seeing others walk or dance, one might dream of doing so.
As for amputees, their phantom limb pains can disappear in dreams because the sleeping brain is almost cut off from sensations coming from the body.
Do sleepwalkers dream?
Yes, sleepwalkers often dream during their episodes, even though the opposite was taught in sleep courses from 1970 to 2006! We now know that 71% of adult sleepwalkers occasionally remember a dream related to their nocturnal escapade, and this dream almost always turns into a disaster scenario.
Sleepwalking affects 4% of adults and runs in families: it is inherited from a parent in nearly 70% of cases. Episodes occur in the first part of the night during deep slow-wave sleep. A lack of sleep or new stress (studying away from home, a first job) is enough to trigger them again. A simple loud noise can also provoke a "crooked" awakening: some husbands of sleepwalkers have learned to slip into bed without making a sound!
In their dreams, sleepwalkers flee: the ceiling collapses, the walls close in, insects invade the bed... Since their eyes are open, these scenes often take place in their own room. These escapes can end badly: a 25-year-old man who dreamed of saving his little niece from drowning jumped out of a third-floor window and broke his pelvis. When the episode is accompanied by screaming, a racing heart, and intense fear, it is referred to as night terrors, a form of sleepwalking.
The sleepwalker may also reenact their day. After her first day of a summer job packing groceries in a supermarket, a 22-year-old student woke up with her alarm clock, boxes, and phone wrapped in her duvet cover! It’s better to avoid violent movies in the evening when you are a sleepwalker.
Some even go so far as to eat while sleeping, a disorder that specialists relate to sleepwalking: 4.5% of the population has eaten at least once during their sleep.
REM sleep behavior disorder: when you fight in your sleep
REM sleep behavior disorder brings dreams to life through actions. The mechanism that normally paralyzes the body during dreams no longer functions, and the sleeper hits, screams, or thrashes, especially after the age of 50 and typically towards the end of the night.
This disorder was only described in 1986 by psychiatrist Carlos Schenck in Minneapolis, who treated men aged 50 to 80 injured in their sleep: one had a broken arm after hitting the wall behind his bed, and another's wife had a black eye.
The explanation had been known since 1962. By destroying the area of the brainstem that blocks muscles during REM sleep in cats, neurobiologist Michel Jouvet produced animals that hunted and groomed themselves while in deep REM sleep.
It is not to be confused with sleepwalking, even though they are often mistaken for each other. The sleepwalker is young, acts early in the night with eyes open, and flees from a catastrophe. The sleeper affected by this disorder has their eyes closed, believes they are being attacked by an animal or an assailant, and fights back with kicks and punches. Beware of anyone sleeping next to them! A husband dreaming of defending his wife against attackers in a forest may end up on the floor after beating up his bedside table, while his wife discovers a bruise on her temple.
One medication, clonazepam, prevents most of these movements. It is advisable to discuss it with a doctor: after the age of 50, this disorder can be the very first sign of a neurological disease.
Dreams in action and Parkinson's disease: a signal to take seriously
When it occurs alone, without any other illness, REM sleep behavior disorder indicates a neurodegenerative disease in 80% of cases five to fifteen years later, whether it be Parkinson's disease or certain dementias. Simple restless nightmares can therefore be the first sign of brain impairment.
The American psychiatrist who described this disorder in 1986 reviewed each of the 27 patients treated between 1986 and 1990 every year. After five years, nearly half had developed dementia or Parkinson's disease. Today, high-risk individuals are identified on average ten years before the first symptoms, at a stage where the brain has lost far fewer nerve cells. This allows for much earlier attempts to protect it: medications, physical activity, coffee, or avoidance of toxic products, all of which are still under study.
Even more surprisingly, patients who are already ill move better in their dreams than when awake. Out of 100 surveyed Parkinson's patients, 60 acted out their dreams. And 87% of their wives found their movements more successful than when awake, sometimes even better than at the best moment of their treatment! Their voices become loud and clear, and the tremors completely disappear. One patient who walked with difficulty and could barely speak thus lifted a heavy oak bedside table in the middle of the night to fend off the caimans in his dream.
If your partner struggles or screams in their sleep, come as a couple to the consultation: it is often the bed partner who best describes what happens at night.
Learning while sleeping: what sleep really does for memory
Sleep does not replace studying, but it enhances it. Students who score 12/20 after intensive training average 16/20 the next morning after a night of sleep. In contrast, those who study in the morning and retake the test in the evening without sleeping drop back to 10/20.
These results, drawn from experiments mainly conducted at Harvard since 2000, have three possible explanations:
Sleep protects recent memory from daily interference.Slow sleep consolidates information in the brain areas that have been active. These areas actually sleep more deeply than others.The brain replays learned sequences at night, like a rat running its maze in its sleep.
And what about dreaming? Students learned a video game, then some took a two-hour nap while others stayed awake: the sleepers performed significantly better afterward, and the highest scores went to those who dreamed about the game. For a sequence of finger movements, speed plateaus during training and then jumps by 30% after a night of sleep, as if the sleeping brain had identified the most frequent patterns.
The takeaway advice is simple: allow for a night, or at least a nap, between learning and testing. Sacrificing your night to study deprives you of this boost.
Nightmares: their usefulness and the method to get rid of them
Nightmares are normal and probably useful, as about three-quarters of our dreams are negative, and these unfortunate scenarios could serve as a rehearsal for facing difficulties. When a nightmare keeps recurring, a simple method allows you to rewrite it.
Medical students know something about this: in a study conducted with a cohort of 2,324 first-year students, over 92% of those taking the exam for the first time had negative dreams. Cancelled flights, delays, blank papers, or having to write an exam on a piece of bread due to lack of paper... it all happened! However, the top ten students in the ranking all experienced such horrible dreams, and their grades were even better the more they dreamed about the exam.
For recurring nightmares, doctors commonly use image-based cognitive therapy:
Upon waking, write down your nightmare (a child can draw it).Read it again later, calmly and in broad daylight, to diffuse its emotional charge.Invent a happy ending for it: if you fall off a cliff, open a parachute. If zombies are chasing you, imagine yourself as a cameraman on a set, facing made-up actors.Read this new version at bedtime, several nights in a row.
Do precognitive dreams exist?
Nothing suggests that dreams predict the future: when researchers investigated, they found no precognition. This does not prevent more than 70% of people from claiming to have had at least one prophetic dream, an impression that can be explained quite well.
Take a classic case: a man dreams of an old acquaintance, whom he hasn't seen in over fifteen years, falling from a roof and dying. Shortly after, he learns that this man has died... by falling from the roof he was repairing. Disturbing? Except that we have countless dreams, mostly negative, and we forget almost all of them. It only takes one event from the day to remind us of a dream for us to feel like we were right... while forgetting the thousands of others that never came true.
Our dreams are also influenced by our daily worries. A mother who often dreams that her children are in trouble may, one day, coincidentally see one of those dreams align with reality. Among medical students surveyed on the evening of their exam, dreaming of failing the test did not increase the risk of actually failing it.
So if you dream of failure or being late, there's no need to panic: this dream reflects your concerns, not your future.
Lucid dream: knowing that you are dreaming (and sometimes directing your dream)
Having a lucid dream means being aware that you are dreaming without waking up, to the point of sometimes being able to steer the storyline. The phenomenon is less rare than one might think: in a survey conducted among 919 German adults, 51% had experienced at least one.
Women and young people are the most affected, but "voluntary" lucid dreamers who have more than five per week remain very rare. People suffering from narcolepsy are an exception: over 77% of them experience lucid dreams (an average of eight per month) and use them to chase away their nightmares.
Scientific proof came from a clever idea: since the body is paralyzed during REM sleep while the eyes move, lucid dreamers signaled their state with a pre-agreed code, such as looking four times in succession from left to right, which was clearly visible on recordings.
Want to give it a try? Several techniques have been studied:
The dream journal, kept every morning and after each nighttime awakening: it strengthens dream memory and helps identify their oddities, making them easier to recognize the following night.The reality check: regularly asking yourself during the day whether you are dreaming, while observing your surroundings.Repetition before sleeping: imagining a scenario that you will pick up knowing that you are dreaming. This method works better if you wake up 30 to 120 minutes before your usual time and stay awake for at least an hour before going back to bed.The intention: at bedtime, strongly envisioning yourself dreaming consciously, in control of your dream. Taught to patients suffering from recurring nightmares, this variant allowed half of them to become lucid dreamers in less than three months.
Commercially available light masks and other sound stimuli have not yet been validated, and lucidity has its limits: the setting and a good part of the story escape the dreamer. For further guidance, our practical tips are compiled in Lucid Dreams: 5 Things to Know Before Trying.
Sleep paralysis and hallucinations: when dreams spill over into wakefulness
Sleep paralysis and hypnagogic hallucinations are fragments of dreams that spill over into wakefulness when REM sleep intrudes at the wrong moment on the border between wakefulness and sleep. As frightening as they may be, these experiences are not a sign of madness.
Sleep paralysis is the horrifying sensation of being paralyzed at the moment of falling asleep or waking up. Hallucinations, on the other hand, mainly occur during the onset of sleep (known as hypnagogic) or upon waking (hypnopompic): sounds of footsteps from an imaginary intruder crossing the room, the feeling of floating above one's bed, or even seeing oneself as a double. They also affect healthy individuals, as six out of ten monks forced to rise in the middle of the night to pray have experienced them.
They are particularly common in narcolepsy, a rare condition (0.02% of the population) where REM sleep occurs immediately upon falling asleep instead of waiting 90 minutes. Nearly one in two narcoleptics (45%) suffers from it, sometimes even while fully awake: one patient reportedly slammed on the brakes in front of a little boy crossing the street... only to realize there was no one there. It also happens that patients convinced they live in a haunted house move to another place... and find their ghosts there.
A few strategies can help tame them:
Understand the phenomenon: when a doctor explains these "waking dreams" to them, patients often feel reassured.Keep a nightlight near the bed, to quickly check that the vision is not real.Consult if episodes recur: in narcoleptics, treatments that suppress REM sleep also reduce hallucinations.
In short: what to remember about dreams
Why do we dream? In the absence of a definitive answer, science has identified solid leads: consolidating what we've learned, digesting emotions, and training for danger. Here are the key points to keep in mind:
We primarily dream during REM sleep, which occurs approximately every 90 minutes, but also during slow-wave sleep.A notebook by the bedside, kept for two weeks, helps remember many more dreams.In dreams, the deaf can hear, paraplegics can walk, and people who have gone blind after five years can still see.Sleepwalkers dream. And dreams acted out that appear after age 50 deserve a consultation.Recurring nightmares can be treated by rewriting their endings. Precognitive dreams, on the other hand, are a matter of chance and our selective memory.
Research continues to advance: a Japanese team interrupted over three hundred instances of volunteers falling asleep in an MRI machine and successfully guessed in 80% of cases whether they were seeing a cake, a car, a woman, or a man. Not yet enough to read your dreams, rest assured... In the meantime, nothing stops you from noting them yourself: a notebook and a pen on the nightstand are enough to start tonight!
Nota Bene: Slow-wave sleep encompasses the stages of light and then deep sleep, with the latter dominating the early hours of the night. REM sleep, also known as rapid eye movement sleep, is the stage where the brain becomes active like when awake while the muscles are paralyzed. Hypnagogic hallucinations occur at sleep onset, while hypnopompic ones occur upon waking.