If the visions were films, they 'd not make a dime. Usually they 're banal, sometimes brief and they're screened for only one viewer. As for the narrative? You 're in a supermarket, it's only Yankee Stadium, shopping with your teacher of second grade until she turns into Ruth Bader Ginsburg. You shoot a bear in the cereal aisle then both of you. Somebody is calling for a rewrite.
Yet dreams are much more complicated than that, so if you have a theory that describes them, then you have it. The ancient Egyptians considered dreams merely as another form of seeing, with trained dreamers serving as seers to help plan battles and make state decisions. The ancient Greeks and Romans believed that dreams constituted equal predictions of future events and visits by the dead.
Sigmund Freud found dreaming an expression of repressed conflicts or impulses that were often sexual in nature-no surprise, this being Freud. Carl Jung took a more rigorous approach, explaining dreams as a kind of "shaped energy," inchoate emotions or thoughts unleashed by the deep subconscious and narrated by higher regions of the brain. Modern psychologists and neurologists, armed with imaging equipment including PET scans and MRIs, took things to a deeper and more technical level, speculating that dreaming is the brain's way of dumping excess data, consolidating important information, keeping us alert to danger and more.
But why do dreams take on the form they make? Why do you keep dreaming after you graduated from college about having to prep for the finals years? How do you dream of soaring, or being chased by a wild animal, or turning up with your always-absent pants at that always-embarrassing party? And why are there such powerful or strange or twisted dreams that you would take them to your grave instead of exposing them to everyone in the world as much as a single detail?
The least glamorous reason for any dream is that it acts as a kind of data dump — clearing the worthless memories of the day and storing the precious ones. Researchers had long suspected that this process, if it exists, would take place between the hippocampus — which controls memory — and the neocortex that governs higher-order thinking.
A study carried out in 2007 at the Max Planck Medical Institute in Heidelberg, Germany, helped to validate this theory: working with anesthetized mice, the researchers found that as the neocortex fires during sleep, it indicated that various regions of the hippocampus had to store whatever information they had in short-term storage. The hippocampus is then prepared for the next day to collect more, while the neocortex determines what to pass to the long-term memory and what to discard. As the data flows through the dreaming mind's computer screen, some of it gets picked up and arbitrarily stitched into the mad quilt of dreams, sometimes only slightly matching the actual substance of the knowledge.
Justice Ginsburg and the bear, say, may come to mind as your brain examines and discards a scrap of news he's gathered about the Supreme Court and the Interior Department. We don't remember most of this evanescent imagery — an estimated 90 percent — which is consistent with the idea of purging as a dream. "We dream to forget," Francis Crick, Nobel laureate, wrote in 1984.
Crick, who is best known and most celebrated as the co-discoverer of DNA, was unlikely to become a leading thinker — or at least a leading provocateur — in dream theory, and what was known colloquially as his "garbage disposal theory" of dreaming in the 1990s attracted many faithful. But most contemporary dream theorists think things aren't that simple. For example, a century of talk therapy experience has shown that far from profiting from losing all our dreams, we also get a lot from dwelling on them and examining them.
"It's not a huge, dramatic effect but it certainly seems that paying attention to your dreams can have positive effects," says Deirdre Barrett, a psychologist at Harvard University, author of The Sleep Committee. That is not to say that dreams don't involve some sorting and clearing of data. "I think there is truth to this notion that knowledge is being processed. We organize items into groups, equate them to other cases, take into account the knowledge that we can remove during the day.
Another view of dreaming comes from the cognitive neuroscientist Antti Revonsuo of the Swedish University of Skövde, who suggested what he calls the Theory of Threat Simulation, arguing that the brain responds to potential future dangers by running fire drills while we are sleeping just to keep us sharp. That may be the root of the recurring vision of not preparing for the finals — with finals as a stand-in to a presentation you have to compose in your adult life for work. To dream of losing any or all of your teeth — recorded by a large number of study respondents — seems to be nervous at the wrong moment to say the wrong thing. This may even be about physical degradation — something we all fear even in infancy.
It's not all that unexpected that the same dream themes occur across different populations and radically different cultures, as what humans have in common is often far deeper and more primal than what we don't. "We share a lot of genetic conditioning and even modern humans are still worried about large animals with big teeth," Barrett says. "Even in tribes that wear very little, the concept of nudity as a social presentation seems universal too. Inappropriate clothing means shame in most cultures.
Problem-solving is a far more productive dreaming function, as the sleeping brain continues to work on jobs that the waking mind handled during the day. In a 2010 study at the Beth Israel Deaconess Medical Center in Boston, 99 people were given the task of navigating through a three-dimensional labyrinth. They were given a 90-minute break during their practice sessions. Some were asked to engage in quiet activities such as reading; others were instructed to try taking a snack. Those who slept and dreamed about the labyrinth showed a tenfold change in the next session relative to the other topics. Something similar happens when students prepare for a test and find that after a night's sleep they have a better mastery of the subject, particularly if they only indirectly dreamed about what they'd learned.
Finally — give Freud his due — dreams seem to be strictly wish-fulfillment. Dreams of flying can be a desire for liberty. Dreams of finding new rooms in your home can express a desire for opportunity or something new. And as for dreams about sex? Often as they're not about, uh, sex. (Brain doesn't always complicate things.
If we didn't dream at all, or at least didn't dream so much, then our nights would probably be quieter and our sleep more serene. But our minds would not be as rich, nor would our brains be as nimble, nor would our wishes be fulfilled so often – if only in vivid fantasies. The dormant brain screening room can often sweat you out, but like all good theaters, it seldom leaves you bored.
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