Mind & Body

Your Nightmares Might Be Helping You Survive

How many times have you woken up in a panic, thinking you slept through an exam or an important meeting, only to check your phone and realize you were just dreaming? It turns out that nightmares like this are just the brain's way of helping you avoid oversleeping. Dreams about stressful scenarios like sleeping through class, fighting with your significant other, or even being chased by a mysterious figure might have evolved to help us to work through our anxieties in a risk-free environment, better preparing us to face our fears in real life.

A Nightmare a Day Keeps Danger at Bay

Our ancestors had nightmares of their own, though their dreams likely featured lions and tigers rather than textbooks and alarm clocks. After noticing that most dreams tend to have more negative emotions than positive emotions, Finnish neuroscientist Antti Revonsuo developed a hypothesis to understand why nightmares evolved. He called it the threat simulation theory.

Revonsuo's threat simulation theory says that dreams often take us through stressful or scary events as a way to prepare for the real thing. By rehearsing threat perception and avoidance in our sleep, we have a better chance of successfully reacting to threats in our waking lives, whether that means running from a hungry animal or making it to 9 a.m. biology.

The threat simulation theory also helps explain why even modern urbanites have the occasional nightmare about being chased through the woods. Over time, humans have learned to fear dangerous animals (and hostile humans), extreme weather events, and social ostracization, all of which pose threats to their survival. Our fear systems have evolved to be especially sensitive to such threats, so these deep-rooted fears are likely to show up in our dreams.

Dreaming for a Better Tomorrow

Your waking life also has an effect on what kinds of threats you face in your dreams. Dreaming of failing an exam is a distinctly modern fear that couldn't have appeared in our ancestors' nightmares, for instance. In a 2005 study, Revonsuo and fellow neuroscientist Katja Valli took this one step further to see if real threatening events someone experiences while they're awake would affect how frequent and severe their dream threats were.

When they analyzed the dream reports of traumatized and non-traumatized children, they found that real-life trauma does, in fact, impact dream threats. Compared to a group of Finnish children who had been raised in a relatively safe environment, Kurdish children from Northern Iraq who faced regular military violence studied reported a greater number of threats in their dreams. Not only were threats they encountered in dreams more severe, but they also recalled more dreams in general. One explanation for this could be that trauma led to increased activation of the children's threat simulation system, which would work as a form of protection against the increased threats in their waking environment.

Animal studies support the idea that dreaming improves survival instincts. A study of REM-deprived rats from 2004 demonstrated that animals who went without dream sleep struggled with survival-related tasks like finding their way through a maze and avoiding dangerous areas in their environment.

But that's in rats. What about in humans? Well, a 2014 study of medical students led by neurologist Isabelle Arnulf looked at a more relatable scenario: the all-too-familiar test anxiety dream. Sixty percent of the students surveyed said they dreamed of the medical school entrance exam the night before the test. Most of these dreams qualified as nightmares, riddled with fear of failing the test, being late, or forgetting answers. No surprise there. But get this: Students who dreamed of the exam actually performed better on test day. It turns out dreams probably do improve our ability to face threats, whether they're saber-toothed or multiple choice.

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Learn more about the science of dreaming in "Why We Sleep: Unlocking the Power of Sleep and Dreams" by Matthew Walker, Ph.D. The audiobook is free with an Audible trial. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Andrea Michelson July 22, 2019

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