How Dreams Reveal Brain Disorders


For 30 years Isabelle Arnulf, head of the sleep disorders clinic at Pitié-Salpêtrière Hospital in Paris, has studied sleep and its associated disorders. During her career, Arnulf, who is also a professor of neurology at Sorbonne University in France, has researched a broad range of sleep conditions: sleepwalking, rapid eye movement (REM) sleep behavior disorder, lucid dreaming, sleep in Parkinson’s disease and hypersomnia, or excessive daytime sleepiness. As part of these studies, Arnulf investigated how these disorders affect dream states. In an interview with Scientific American’s French-language sister publication Pour la Science, the neurologist talks about whether depression or trauma affects dreaming and whether one should worry about recurring nightmares.

[An edited transcript of the interview follows.]

Our dreams are often bizarre and disturbing and are sometimes frightening. Do some betray a pathology?

Attempts have been made to identify “dream types” that are characteristic of various mental disorders, but this has not gone very far. People with a psychotic disorder, especially people with schizophrenia , have particular dreams that resemble their way of reasoning during the day—flat, disjointed, limited and undiversified content that portrays the dreamer in everyday life situations. Autistic patients also have fairly lackluster dreams, but the reverse is not true; it is not because you have this kind of dream that you are autistic or schizophrenic. In other words, dreams alone are not enough to diagnose mental illness. Some of the characteristics of a dream may yield some hints, however. For example, the frequency of nightmares is generally higher in people with a mental disorder, whether depression, anxiety or post-traumatic stress disorder.

Could frequent nightmares provide a warning about a person’s mental health risks?

The link has been particularly well established with the risk of suicide among young people, which has been on the rise in recent years. Doctors are wrong half the time about projecting someone’s suicide risk. This is why recurrent nightmares have recently begun to be included in the diagnosis because they are correlated with a higher risk of suicide. The stakes are high, because this would make it possible to direct young people with depression to get help earlier with programs such as VigilanS, coordinated by Guillaume Vaiva at the Lille University Hospital in France, which monitors people who have attempted suicide to prevent repeat attempts.

Are there specific qualities that characterize the nightmares of depressed people?

In depression, dreams are very negative, mirroring the mental state of depressed people during the day. This parallel was brought to light in the early 2000s by researcher Dieter Riemann and his colleagues at the University of Freiburg in Germany. By analyzing the dreams of depressed patients treated with antidepressants, they discovered that as the treatment began to take effect after several weeks, the content of these dreams became less and less gloomy, and the mood of the patients improved.

At first glance, one might think that the overall tone of the dreams reflects the depressed state of the patient. But things are not so simple, unfortunately, because in the first weeks of treatment, antidepressants often suppress REM sleep—the phase when we dream the most—and it usually takes a month for patients to remember their dreams again. It’s difficult to understand the link between dreams and depression and to know which of the two is influencing the other. To better understand this link, we can study two categories of dreamers—those who have what are called lucid dreams and people with REM sleep behavior disorder (RBD).

What is special about these dreamers?

In RBD, which we have been studying for 15 years, patients try to implement the actions in their dreams: some eat an imaginary sandwich while sleeping, and others struggle in bed, grappling with invisible adversaries. This enactment is usually caused by a lesion of the brain stem, which means that their movements, often inhibited in a normal dream, are not blocked during REM sleep. And this, unfortunately, involves the risk of accident or injury for them or, [say], their spouse because they do not control what they are doing. But this phenomenon also offers direct access to dreams, much more than the often imprecise stories that sleepers tell when they wake up if they remember [their dreams].

What about lucid dreamers?

They actually recognize that they are dreaming without waking up. As a result, it is possible to agree beforehand on a code for them to communicate certain information to us during their dreams.

In one experiment, we asked lucid dreamers to find a swimming pool in their dream and to turn their eyes to the right twice when they dipped underwater and when they emerged. We have thus shown that our breathing during sleep reflects how we breathe in our dreams; the periods spent underwater corresponded to remarkable apneas of the sleepers! But of course, these types of signals are not always easy to arrange in certain dreams—for instance, in an intense sequence of dream events like a chase. Today we try to use simpler signals, asking the dreamer to punctuate the pleasant parts of their dreams with three small smiles and the unpleasant parts with three slight frowns, which we capture with electrodes placed respectively on the zygomaticus muscles and on those of the forehead.

These two categories of dreamers, in any case, offer privileged access to dreams. If we could find a few who suffer from depression—which is what our team member Jean-Baptiste Maranci of Pitié-Salpêtrière Hospital is trying to do—then we would have a unique way of studying the links between dreams and mood.

What form would a study take?

One of the characteristics of depressed people is that they wake up sadder in the morning than in the evening, whereas normally it’s the opposite: we tend to be happier when we wake up than when we go to sleep. We therefore believe that sleep and dreams serve to attenuate negative emotions and that this process is dysfunctional in people with depression. Maranci’s project consists of identifying markers associated with positive and negative feelings experienced in dreams, among all the signals recorded in the sleep laboratory. A sudden feeling of joy could, for example, result in a change in cerebral activity that is associated with particular eye movement and increased heart rate and breathing. We conducted this research “live” in lucid dreamers who communicated their emotions through signals agreed on with the team of experimenters. Our idea is then to use artificial intelligence for the analyses in order to take into account a large number of parameters.

After this first phase, we will try to find the emotional markers identified in sleepers like you and me. The goal is to better understand how we regulate our emotions during sleep and how quickly we relive and “digest” negative emotions. Then the same research will be carried out in depressed people in order to determine why this mechanism works badly in them.

What is the “emotional digestion” in dreams?

Matthew Walker, a professor of neuroscience and psychology at the University of California, Berkeley, has suggested that the function of sleep and dreams is to degrade emotional memories of the day—to reset the amygdala (the brain region where the emotions are experienced) to preserve the memories associated with the emotions but without the emotions themselves. This is currently the leading theory.

According to Walker, dreams are a kind of mental theater where we relive the trials that have happened to us but integrated into more or less crazy scenarios. The peculiarities of dreams make this repetition of a day’s events easier to live with. Difficult events are replayed without the physical manifestations of strong emotions. Researchers have observed, for example, sleepers who suffered horrors in dreams (as evidenced by the stories they shared when they woke up). But they didn’t show the slightest quickening of a heartbeat. On the other hand, these events are sometimes mixed with positive or bizarre elements. You might be reprimanded by your boss in the dream when suddenly a kitten comes to lick his ear, which lessens the emotions you’re experiencing in the dream.

In the end, this reexposure to the events of the day could lead to the progressive extinction of negative emotions. In our brain, a dialogue occurs between the amygdala, which is very strongly activated during REM sleep, the hippocampus, where the information of the day is stored, and the neocortex, the seat of long-term memory. Thanks to this three-way dialogue, the brain stores the new information by ridding it of its emotional context to consolidate it in a more definitive way in the neocortex.

Do you mean that negative dreams are good for us?

Yes, absolutely. But be careful; it is believed that in nightmares, this beneficial mechanism malfunctions to the point of interrupting the dream in progress and waking the sleeper, so the process of emotional integration cannot go to the end. Why does the sleeper wake up? There are several possibilities. Maybe the person was just sleeping badly, or the emotional intensity of the nightmares was too strong. This is particularly the case in post-traumatic stress disorder, following various types of extreme ordeal—torture, war, rape. The emotion to be appeased is then so violent that the brain cannot manage it. It constantly repeats the traumatic memory, which awakens the sleeper. Finally, about 5 percent of the population has had nightmares since birth without anyone knowing how to explain it.

How should one react to a recurring nightmare?

For a long time, we approached recurring nightmares through the prism of psychoanalysis, [which explained them as] unresolved trauma that we would have to work to resolve. But the fact is: we don’t know.

In the case of repeated nightmares, before going to see a psychologist, in my opinion, it is necessary to make a medical diagnosis rather than be diverted down the wrong pathway. When I started my research, a journalist from Le Monde came to see me for a sleep apnea screening. In the course of the conversation, he told me that he has been having the same nightmare for 10 years in which he was sticking his head through the neck of a bottle and choking. With his psychoanalyst, they came to the conclusion that he was reliving his birth. In fact, he was really choking, with one apnea incident each minute of sleep each night. We offered him a CPAP [continuous positive airway pressure] machine, and the nightmares were gone the first night!

In some cases, a psychological origin can be involved. We have bad dreams during a stressful period, probably because the brain has a greater need to digest negative emotions and wants to simulate the threats we face, which is another purported function of dreams.

In general, there are many forms of nightmares, which have different origins and which a doctor will be able to differentiate. Young people who scream at night and sometimes get out of bed are thus subject to night terrors, a disorder that is similar to sleepwalking but that is not associated with mental health problems. Others [experience] a phenomenon of half awakening called “sleep paralysis”: a very unpleasant moment when the sleeper tries to wake up without being able to move, often with the feeling that a harmful creature is crushing their chest or that the person is possessed by a demon. Lack of sleep facilitates this phenomenon. Others who suffer from RBD make the motions of fighting in their bed to defend themselves against lions or attackers. Some nightmares are caused by drug treatments, for which a doctor can offer alternative medications. So it is necessary to exclude each of these possibilities before starting a therapy targeted specifically for nightmares.

Nightmares are not inevitable. We have to stop thinking that all it takes to stop a round of nightmares is to have things go well when we’re awake during the day. Bad nights themselves produce an unpleasant feeling in the morning, and people then fear going to bed and repeating the same scenario, which maintains this vicious cycle. This was shown by several British and North American teams as early as the 1980s. So tackling bad dreams is a therapy in itself that is actually effective.

What are some of the treatments for nightmares?

Techniques such as mental image rehearsal, as well as drug therapies, are highly effective, according to at least one review of scientific literature. The principle is to slightly modify elements of the nightmare and mentally visualize the new scenario before falling asleep. To give you an example, a patient abused by a priest at the age of 11 who came to consult me for another problem told me that she dreams every night that a devil in a red cassock wants to rape her. I suggested that she try to imagine something happening to the devil, perhaps his foot tripping over his cassock or something else. She decided that a large crucifix would fall on him. By mentally repeating this new scenario in the evening, she managed to transform her nightmare and calm herself.

Confronting the bad dream is therefore therapeutic on its own. Although, I repeat, it is better to start by consulting a doctor, ideally a sleep specialist, in order to exclude a number of organic causes. This is all the more important because certain types of dreams point to neurodegenerative pathologies, such as Parkinson’s disease or Lewy body dementia.

Are there dreams that can help diagnose neurodegenerative diseases?

Agitated dreams—those in which patients mimic everything they are experiencing in a dream—are characteristic of RBD. More than 80 percent of patients suffering from this disorder develop a neurodegenerative pathology within 10 to 15 years of the onset of RBD. Most often, it is Parkinson’s disease. In fact, the brain’s failure to inhibit movements during dreams is a sign that the brain is already beginning to be damaged because [this phenomenon] results from the damage to the area of the brain stem that normally inhibits movement. It is therefore a very strong warning sign.

But we must be careful not to confuse this disorder with somnambulism. In RBD, the affected person is rather restless at the end of the night, is generally more than 50 years old and does not get out of bed, whereas a sleepwalker often wanders around the house and is often much younger. Sleepwalking does not signal any hidden disease, neither neurological nor psychiatric. The studies that have investigated it have just observed that patients are slightly more anxious than average.

In general, do people with Parkinson’s have different sorts of dreams?

According to a 2011 study at Egas Moniz Hospital in Lisbon, their dreams have a more aggressive tone and more often involve animals. In addition, the unusual qualities of their dreams appear to correspond to damage in their frontal lobes.

What about people with Alzheimer’s disease?

The difficulty is that they remember their dreams less. In addition, because their cortex is damaged first, the characteristic patterns of sleep are less discernible on their electroencephalograms, which complicates research. Many also awaken early, which doesn’t make things any easier. We only know that there is no physical acting out, unlike in dreams of RBD patients.

This information is crucial because it makes it possible to distinguish Alzheimer’s disease from another pathology, Lewy body dementia, which represents the third leading cause of dementia globally, after Alzheimer’s disease and vascular dementia. Affecting up to 5 percent of the [older people in the] general population—30 percent of dementia cases—it is manifested by cognitive losses similar to those observed in Alzheimer’s disease and is often confused with it. But [Lewy body dementia] is accompanied by RBD, which is not the case with Alzheimer’s disease. As a result, this readily available biomarker can distinguish between these two dementias, and it is necessary to avoid giving neuroleptics (antipsychotics) to people with Lewy body dementia (which is sometimes done for an Alzheimer’s patient but can be toxic if it is administered to patients with Lewy body disease).

Dreams are therefore likely to provide valuable information about our mental and neurological health. They are still not made use of enough because they have long been the preserve of psychoanalysis. But things are progressing: more and more doctors are interested in them, having understood that taking them into account can help in diagnosis.

This article originally appeared in Pour la Science and Cerveau & Psycho and was reproduced with permission.


If you or someone you know is struggling or having thoughts of suicide, help is available. Call or text the 988 Suicide & Crisis Lifeline at 988 or use the online Lifeline Chat.


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