Popular Science

How the mind concocts dreams and nightmares


YOU DREAM FOR TWO HOURS every night, but for something so common, it’s a remarkably enigmatic process. Only in the past few decades, with the advance of technology like fMRIs that lets us record and visualize activity in the brain, have neuroscien­tists begun to figure out how and why we experience these reveries. While sleepy interludes seem to rely on many of the same mental processes we use while awake, researcher­s are still trying to understand the way they work together during slumber. Here’s how we think our brains drive our nocturnal hallucinat­ions.


Dreams tap memories stored in connection­s between brain cells, which the hippocampu­s tracks as they form. At night it directs neurons to replay recollecti­ons, facilitati­ng longterm storage. That could be why reality seeps into our visions—but not why they tend to warp reality.


Our most vivid imaginings occur during the REM phase of sleep. Activity increases in brain regions that control movement and process optical inputs, like the visual and motor cortices, which likely create what we “see” and “do” in slumber. It’s not clear what triggers these areas at night.


The almond-shaped amygdala helps generate feelings like fear, anger, and anxiety. It and other emotional domains are more rowdy during REM sleep, which could explain why strong reactions happen frequently when we doze. We may rely on this process to dull the sting of difficult memories.


Despite their disjointed nature, dreams still contain semiration­al thoughts, likely thanks to areas supporting conscious cognition. The anterior, or front, portion of the cingulate, a semicircle in the brain’s center, influences motivation and decision-making—and can switch on while we’re snoozing.


During REM, neuroscien­tists see suppressio­n of the dorsolater­al prefrontal cortex, which is critical for executive functions like directing attention, solving problems, and reasoning. This might help explain why we rarely realize we’re asleep, despite some outlandish scenarios.

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