Why do we dream?

Why do we dream?

Amanda Gefter writes:

In the late nineteen-nineties, a neuroscientist named Mark Blumberg stood in a lab at the University of Iowa watching a litter of sleeping rats. Blumberg was then on the cusp of forty; the rats were newborns, and jerked and spasmed as they slept. Blumberg knew that the animals were fine. He had often seen his dogs twitch their paws while asleep. People, he knew, also twitch during sleep: our muscles contract to make small, sharp movements, and our closed eyes dart from side to side in a phenomenon known as rapid eye movement, or rem. It’s typically during rem sleep that we have our most vivid dreams.

Neuroscientists have long had an explanation for our somnolent twitches. During rem sleep, they say, our bodies are paralyzed to prevent us from acting out our dreams; the twitches are the movements that slip through the cracks. They’re dream debris—outward hints of an inner drama. Human adults spend only about two hours of each night in rem sleep. But fetuses, by the third trimester, are in rem for around twenty hours a day—researchers using ultrasound can see their eyes flitting to and fro—and their whole bodies seem to twitch. When a mother feels her baby kick, it may be because the baby is in rem sleep. Once born, babies continue to spend an unusual amount of time in rem, often sleeping for sixteen hours a day and dreaming for eight.

Increasingly, these facts struck Blumberg as odd. In adults, dreams are offshoots of waking life: we have experiences, then we dream about them. But a baby in the womb hasn’t had any experiences. Why spend so much time in rem before you have anything to dream about? According to the dominant theory, the rats’ twitching eyes were supposedly looking around at dream scenery. But the rat pups were just days old; their eyelids were still sealed shut, and they’d never seen anything. So why were their eyes—and their whiskers, limbs, and tails—twitching hundreds of thousands of times each day?

Blumberg decided to put the dream-debris theory to the test. He surgically removed the rats’ cortex—the brain region, involved in visual imagery and conscious experience, where dreams were believed to originate—leaving only the brain stem, which controls subconscious bodily functions, intact. The sleeping pups continued to twitch exactly as before. “There was no way that twitching was a by-product of dreams,” Blumberg told me, when we spoke last fall.

Now in his sixties, Blumberg is the chair of the Department of Psychological and Brain Sciences at the University of Iowa. He has spent the past twenty years studying sensorimotor development—the process through which an infant’s brain links up with its body. Twitches had long been overlooked by sensorimotor researchers. “If you’ve been told since Aristotle that they’re remnants of dreams—well, who wants to study a remnant?” he said. But, in fact, the science of dreams was far from settled. Freudians believed that they contained repressed wishes dredged from the dark corners of psychic life; many neuroscientists have seen them as random brain chatter. Some theories have suggested that dreams consolidate our memories, others that they help us to forget. With twitches, Blumberg had identified a new thread in the mystery of dreaming. By pulling, could he unravel the whole? [Continue reading…]

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