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"The dream is real." So goes the tagline of Inception, the latest big-budget head-trip from Christopher Nolan, the man behind Memento and The Dark Knight. But, of course, the science isn't.

And yet, despite the movie's preposterous vision of architects constructing dreamworlds and multiple sleepers slipping into these collective unconscious spaces, Inception draws on certain popular beliefs about dreams that are based in actuality. Whether it's adopting fundamental theories about the function of dreams as psychic manifestations of our emotional lives, or taking on recurrent dream memes—such as being pursued, killed, or falling—as plot devices, there's a lot that Inception gets right.

Dream scholar Kelly Bulkeley, a Visiting Scholar at the Graduate Theological Union and a faculty member at John F. Kennedy University whose books include An Introduction to the Psychology of Dreaming, claims the film's central conceit—that dreamers can become active, controlling participants in their dreams—is backed up by research. "Lucid dreaming," as it's known, is a reality, according to Bulkeley, who points to a May 2010 poll he conducted with Zogby Interactive whose results suggest that volitional control within the dream state turns out to be a relatively widespread phenomenon. (Of the 2992 American adults who were randomly selected to complete an online survey, 34.4% said they had experienced the ability to control what happens in their dreams.)

The poll reaffirms what Dr. Stephen Laberge and his colleagues Lynne Levitan and William Dement at Stanford University's Sleep Research Center have long suggested with their dreaming studies: by conducting experiments on volunteer sleepers and examining rapid eye movements, EEG readings, and detailed interviews with their subjects, Laberge believes, as he writes in his 1985 book Lucid Dreaming, that conscious dreamers can "create and transform objects, people, situations, worlds, even themselves. By the standards of the familiar world of physical and social reality, they can do the impossible."

"In the past, there was a very sharp dichotomy between ideas of rational waking consciousness and crazy, dreaming consciousness," Bulkeley explains. "Now we're realizing that's not the case at all. We believe that within the dream space, we can become aware, conscious, and make decisions."

The film also draws its main conflict from an area of dream research that may feel old-hat but is still upheld by most experts: that traumas or guilty feelings often come out in dreams and disrupt the dreamer.

If that sounds like old-fashioned Freudian psychoanalytic theory, Bulkeley calls the concept an "oldie, but a goodie." He adds: "As far back as you want to go, people have been having dreams about guilty feelings about their past moral failings. Mourning what's been lost is also a powerful theme in dreams," which certainly reflects the dreams that plague Inception's protagonist Dom Cobb (Leonardo DiCaprio) and Cobb's mark, an energy magnate heir (Cillian Murphy) whose father has recently died.

Harvard Medical School psychologist and dream expert Deirdre Barrett, who edited the book Trauma and Dreams, agrees. "You can demonstrate that people who have traumas have nightmares and that trauma can come back and reoccur in nightmares. That's pretty inarguable." She adds, "It would likely start showing up and potentially interfering in the way that you're trying to focus or shape the dream." Inception illustrates this effect vividly when a massive freight train, a potent symbol for Cobb's guilty conscience, shows up uninvited in the middle of a highly planned-out dream scheme.

But Barrett also suggests such traumas don't always manifest themselves in dreams. "It's certainly not all of the content. Most people who have experienced trauma have unpleasant dreams, but some people don't."

In that sense, Inception's basic psychological premises and conflicts rest more on generally held beliefs than on scientific proofs.

"Even in the professional culture, it's very hard to prove" such ideas, says Tufts University psychiatrist Ernest Hartmann, the author of Dreams and Nightmares: The New Theory on the Origin and Meaning of Dreams. But based on clinical studies, he says, "it does seem to me that the dream makes connections that you don't make in waking. It's not necessarily about guilt, but you're more broad-minded and open to possibilities. Dreaming is the most connective, creative part of our mental functioning, so in that sense, we do work things out; we do gain insights."

Where Inception falls particularly short is in the specific rules of the game. For instance, being killed in a dream doesn't always waken the dreamer; dreams within dreams are extremely rare (according to Barrett, "less than 1 percent" of dreams); and the majority of recalled dreams generally "map onto real time," says Barrett; for example, the longer a person has been in REM sleep, the longer the dream will seem, most lasting a few to 15 minutes—and not the experience of hours or even decades that Inception imagines is possible.

Even less credible is the way Inception plays out the process of "extraction" or "inception," in which Cobb steals or implants corporate secrets from people's minds by inserting an electrical cord into their arms and entering the dreamworld. Here, we're not so far off from the "neurological synaptic transfer system" of 2000's The Cell or even the way characters are psychically projected into other people's dreams in 1984's Dreamscape.

According to Barrett, extracting information from surface electrodes attached to the brain is not completely impossible: for instance, EEG readings can determine whether the human brain is making mathematical calculations or practicing skilled athletic activities during sleep. And in a 2006 MIT study, scientists proved that rats who were trained to run mazes would then rehearse the mazes while sleeping, turning right and left in the animal equivalent of dreams. "We can't get that precise with humans," says Barrett. "We may eventually get better, but I don't think we're ever going to figure out how a complex thought maps on a brain firing pattern."

Of course, few moviegoers will expect such verifiable science from Hollywood's "dream factory." And it may be unfair to judge Inception on its scientific merits since so much about dreams remains a mystery. As Christopher Nolan himself has acknowledged, "The brain is capable of more than we'll ever know."