The premise put forth in "Inception" seems fantastical, other-worldly, something out of Big Brother -- the idea that someone can penetrate another's subconscious to extract information or plant an idea.
But according to experts versed in the science of dreaming, the notion is closer to reality than sci-fi.
In the Christopher Nolan film that hits theaters today, Dom Cobb (Leonardo DiCaprio) and his cohorts attempt to plant an idea in the mind of the would-be heir to an energy conglomerate, a process called "inception." Cobb already excels in "extraction" -- in which he invades his targets' dreams and steals information -- but inception presents an entirely new challenge that makes for a blockbuster story.
The science behind Nolan's film is equally fascinating. Nolan takes the concept of lucid dreaming -- a dream in which the subject is aware that they're dreaming and can manipulate the dream -- and runs with it. Throughout the movie, Cobb forces himself to sleep by attaching his arm to a machine that looks like a vaguely ominous reel-to-reel tape player. He retreats into his dream world to reconnect with his deceased wife, Mal, effectively putting his memories of her on repeat.
That can happen in real life through the practice of self-suggestion.
"If you tell yourself, 'Tonight when I dream, I want to realize that I'm dreaming,' or, 'Tonight, I want to dream about my deceased wife,' or, 'Tonight I want to dream my next great masterpiece' -- whether it's to solve a particular problem or if it's to see a person you want to see or a place you want to see, that's the single most powerful technique," said Deirdre Leigh Barrett, professor of psychology at Harvard Medical School and editor of "The New Science of Dreaming."
Controlling one's dreams has been possible for centuries -- Tibetean Buddhists practiced it 1,000 years ago; so did yogis. Nolan himself began practicing lucid dreaming and dream manipulation as a teenager and mined his own dreams to conceive "Inception."
"I wanted to do this for a very long time, it's something I've thought about off and on since I was about 16," Nolan told The Los Angeles Times last year. "I wrote the first draft of this script seven or eight years ago, but it goes back much further, this idea of approaching dream and the dream life as another state of reality."
Figuring out what a sleeping person is dreaming about is possible as well. Cognitive neuroscience techniques allow researchers to view three-dimensional brain scans as they happen, and methods of monitoring the subconscious continue to advance.
"The potential to image human brains non-intrusively is growing," said Barrett. "We already see content like, it looks like a person is working on math. Or the language centers are very active. It's not impossible that we would eventually have some technology to both manage what's going on in a dream and influence what people dream about."
What's more murky is the idea of dream-sharing -- that several people can engage in the same subconscious experience. While groups of dream sharers exist, evidence of dream sharing is more anecdotal than evidential.