science commentary


Nightmares are the brain's way of dealing with traumatic memories.

by T.J. Nelson

science commentary

I t's become a cliché in the popular press to call every scenario you don't like a nightmare. For instance, last night I dreamed that there was some guy with strange hair who owned a great many buildings and kept telling us things were going to be ‘tremennnnnndous!’ There are probably hundreds of articles on the Internet calling The Donald or his nemesis, Hill, a ‘nightmare.’

But nightmares are no laughing matter to people who have them. What may start out as a nice idyllic dream, like a walk through a shady forest, can turn into something so terrifying that the viewer wakes up in a panic. The images can be so disturbing that they are impossible to forget. Nightmares can lead to depression, change your perceptions of the world, and interfere with your daily life. Distorted MRI brain image

Night­mares are the brain's way of presenting a situation in your life it finds distres­sing. It does this by stripping whatever narrative your conscious mind imposes on it. Details may be added, removed or changed; cause and effect may not seem to apply. Only the emotional content is retained. The purpose of nightmares is to help you recognize and resolve a problem in your life—to warn you about something. They are common in periods of life stress.

Nightmares are powerful because they're telling you something true. That is not to say that a nightmare is a true representation of your true nature or your real situation. But it is a true representation of how the brain feels. By its very existence, a nightmare is proof that the brain feels that there is, in fact, some problem in your life. But what?

Post-traumatic stress disorder

Nightmares are especially common in people suffering post-traumatic stress disorder (PTSD) such as that experienced after combat.[1] Women in combat are twice as likely as men to get PTSD.[2] According to T.C. Smith[3], 7.6–8.7% of combat deployers experience PTSD, which is three times higher than among military personnel who did not experience combat. Up to 90% of combat veterans have trauma-related nightmares that can last for years.[1] The occurrence of nightmares after a traumatic incident may presage the onset of PTSD.

Patients with PTSD have elevated levels of norepinephrine[4], possibly caused by overactivity in the amygdala, the part of the brain responsible for dealing with aggression and fear. Although depression is a common symptom, combat-related PTSD is not a form of depression and does not respond to SSRIs.[5] Alpha-1 adrenergic antagonists like prazosin are effective, and prazosin is commonly prescribed for PTSD.

Another treatment is imagery rehearsal therapy[6,7] where the patient is told to write down the dream with a different, better ending, and think of the dream during the day. The idea is that the new, improved dream will replace the old one.

Stress may trigger the conversion of ordinary dreams, which are often about mundane topics, into nightmares. By definition a nightmare is a dream that that wakes you up and produces a disturbing emotional feeling, usually fear, anxiety, sadness, or horror. About 4% of the adult population has nightmare disorder, in which the same nightmares are repeated over and over.

Theories about nightmares

Some researchers, including Antti Revonsuo, believe nightmares are threat simulations whose purpose is to rehearse potential strategies[8] and thus serve a problem-solving or adaptive function. Tore Nielsen and Ross Levin[9] proposed that four brain regions (the amygdala, medial prefrontal cortex, hippocampus, and anterior cingulate cortex) work together to extinguish fear-inducing conditioned responses and that nightmares are the brain's way of working to eliminate fear memories that are no longer useful.

A phenomenon called image contextualization, that is, adding images that place the fear memory in some situation, plays an important role by producing images that activate the emotional content. Ernest Hartmann postulated that contextualization builds up new memories that help to integrate the traumatic memory. Nielsen and Levin proposed that their purpose is not to integrate the traumatic memory, but to extinguish it by creating images that are incompatible with the harmful memory, thereby gradually erasing it.

A simple way of putting it is that a nightmare is the brain's way of taking out the garbage.

Interpreting nightmares

What's relevant in any dream is not the actual images, but the emotional content. That's true for nightmares as well. Characters in a dream might not even represent real persons—they can represent character traits of the dreamer or even abstractions. There are many books and websites claiming to help you figure this stuff out, but the only one who can really interpret a nightmare is the one who experiences it and who knows what the images mean to the dreamer.

That said, some common types of nightmares are easy to understand. If someone dreams about being chased, it often means they are trying to avoid something in real life. If they dream of being naked on the day of a test, it often means they're not preparing for something and their brain is warning them their lack of preparation will be exposed at a critical moment. The brain is saying: you're going to feel exposed, as if you're naked.

But what if you're dreaming about having sex with Angela Merkel? In that case that nightmare is your brain's way of telling you you are one sick, sick puppy and you should be utterly and totally ashamed of yourself.

The brain has a remarkable ability to figure things out from insufficient evidence. This is in the job description for some people, like scientists and car mechanics, but it's also true for everyone. Sometimes the warning may be quite literal: if you dream about you or a friend being injured or getting a fatal disease, you should take the warning seriously.

The value of nightmares

Dreams can affect your work, your friendships, and even your political views. Thus it's important to recognize what they mean. It's valuable information that we can't get any other way.

Dreams are an amazing bit of programming that we should be profoundly grateful for. If the rest of the body could provide meaningful information about what's really going on in our physical bodies, as dreams do for our minds, we might never need to visit a doctor.

It's believed that all mammals experience nightmares, but reptiles and lower animals like insects do not. This doesn't necessarily mean dreams are essential for mental function, but it does mean they provide an important survival value. Of course one can have too much of a good thing, but just the act of trying to figure them out can lead to greater insight about one's own life. As Raymond Lloyd Richmond writes, a dream is always telling you to wake up. “An event is traumatic because it disrupts your previously secure—and illusory—sense of ‘self.’ And so, to heal from a trauma, you must take the initiative to make conscious changes in your life.”

And maybe that's why nightmares wake us up—they're the brain's way of making sure you get the message—and remember it—whatever the cost.


[1] J Neuropsychiatry Clin Neurosci. 2014 Winter;26(1):24–33. Prazosin for military combat-related PTSD nightmares: a critical review. Writer BW, Meyer EG, Schillerstrom JE. Abstract

[2] Epidemiology. 2008 May;19(3):505–512. Prior assault and posttraumatic stress disorder after combat deployment. Smith TC, Wingard DL, Ryan MA, Kritz-Silverstein D, Slymen DJ, Sallis JF; Millennium Cohort Study Team. Abstract

[3] BMJ. 2008 Feb 16;336(7640):366–371. New onset and persistent symptoms of post-traumatic stress disorder self reported after deployment and combat exposures: prospective population based US military cohort study. Smith TC, Ryan MA, Wingard DL, Slymen DJ, Sallis JF, Kritz-Silverstein D; Millennium Cohort Study Team. Abstract

[4] Geracioti TD Jr, Baker DG, Ekhator NN, et al: CSF norepinephrine concentrations in posttraumatic stress disorder. Am J Psychiatry 2001; 158:1227–1230.

[5] Lydiard RB, Hamner MH: Clinical Importance of Sleep Disturbance as a Treatment Target in PTSD. FOCUS The Journal of Lifelong Learning in Psychiatry 2009; VII:176–183.

[6] Behav Ther. 2010 Jun;41(2):237–244. Effectiveness of imagery rehearsal therapy for the treatment of combat-related nightmares in veterans. Nappi CM, Drummond SP, Thorp SR, McQuaid JR. Abstract

[7] J Clin Sleep Med. 2010 Aug 15;6(4):389–401. Best practice guide for the treatment of nightmare disorder in adults. Aurora RN, Zak RS, Auerbach SH, Casey KR, Chowdhuri S, Karippot A, Maganti RK, Ramar K, Kristo DA, Bista SR, Lamm CI, Morgenthaler TI; Standards of Practice Committee; American Academy of Sleep Medicine. Abstract See also here.

[8] Revonsuo A. The reinterpretation of dreams: an evolutionary hypothesis of the function of dreaming. Behav Brain Sci 2000;23:877–901.

[9] Sleep Med Rev. 2007 Aug;11(4):295–310. Nightmares: a new neurocognitive model. Nielsen T, Levin R. Abstract

See also:

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