Having nightmares may help to prepare us for potentially frightening situations, a study at the University of Geneva and University Hospitals Geneva, and the USA’s University of Wisconsin, has found.


There’s a huge amount science still doesn’t know about dreaming. It’s not even clear if everyone does it: we know that everyone experiences REM sleep, but whether those who claim they never dream really don’t, or do dream but simply don’t remember it after waking, isn’t clear. Nor is the mechanism by which dreams are formed in the brain entirely understood, never mind why it happens.

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However, many neuroscientists have long believed that bad dreams allow us to safely ‘act out’ potentially dangerous situations before they occur in real life. And the new findings seem to add weight to that theory.

The researchers asked 18 volunteers to wear EEG headsets while they slept and then woke them multiple times during the night to ask them a series of questions about whether they’d been dreaming, and if that dream involved fear. They then compared the volunteers’ answers to their mapped brain activity during sleep.

They discovered that during ‘scary’ dreams, two areas of the subjects’ brains were particularly active: the insula and the cingulate cortex. During the day, the insula is involved in identifying and evaluating emotional responses, while the cingulate cortex is responsible for preparing the body’s physical reaction to perceived threats (the famous ‘fight or flight’ response).

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A patient with a high-density electroencephalogram (EEG), which measures brain activity during sleep using numerous electrodes placed on the skull © Baumann, Dorothée
A patient with a high-density electroencephalogram (EEG), which measures brain activity during sleep using numerous electrodes placed on the skull © Dorothée Baumann

In the second part of the study, 89 participants kept a ‘dream diary’ for a week, and were then shown a series of distressing images while lying in an MRI scanner. In subjects who reported having a lot of frightening dreams, the images triggered less of a response in the two brain regions studied, and in the amygdala - the brain’s ‘fear centre’ - than patients who reported few or none. What’s more, patients who’d had more bad dreams showed more activity in the medial prefrontal cortex, a region of the brain that’s known to ‘dampen down’ the fear response.


“Dreams may be considered as real training for our future reactions, and may potentially prepare us to face real-life dangers,” said lead researcher Lampros Perogamvros, a senior lecturer in the Center for Sleep Medicine at University Hospitals Geneva.


Russell Deeks is a freelance writer with nearly 30 years’ journalism experience, working across the fields of music, technology and science – which, he says, cross over more often than you might think. Despite the drawback of holding a degree in English & American Literature, he has been a regular contributor to BBC Science Focus since 2006.