In the movie Inception, Leonardo DiCaprio invades other people's dreams. He creates dreamscapes, steals information, and implants ideas. I thought the movie was brilliant. Of course, like any science fiction story, the movie violated some aspects of current science. Creating dreams for other people, however, may actually be possible - Inception, the science.

Sharing dreams would be way cool. Currently conscious experience is a private experience. You can't see my thoughts and I can't see yours. William James made this argument about consciousness over 100 years ago. He noted that when Peter and Paul both wake up in the same room, they reach back to their own streams of thought interrupted by sleeping. They don't get confused about whose past is whose or which thoughts belong to which man. Another person's thoughts do not leak into your head. Of course, we can sometimes see what another person is thinking - we watch their behavior and follow their eye gaze (see my earlier post on Mind Reading Children). But sharing dreams is beyond the current capabilities of science (which is a shame because it certainly looked like a lot of fun).

Giving people dreams, however, is possible. We can create a form of dream and idea inception even without the cool devices used in the movie. In the movie, they paid homage to one method for successfully implanting ideas and dreams. When asked about giving people ideas, one of the characters noted that it is easy - just tell them to not think about something, like don't think about an elephant. Telling people to not think about something is what Daniel Wegner and his colleagues have been doing for years. In their classic work, they told people to not think about a white bear. Wegner has found that when people try to suppress a thought, they end up thinking about it more afterwards. Wegner refers to this as a rebound, or white bear, effect. The thought of a white bear rebounds after you try to suppress it.

Using the white bear effect, we can create dream inception. Attempts to suppress an idea will lead to the idea appearing in your dreams. Wegner, Wenzlaff, and Kozak used the rebound effect to cause people to dream about a particular person. First, they asked people to think about one person: either someone on whom they had a crush or someone they liked but weren't romantically attracted to. Next Wegner and colleagues gave people instructions for a thinking task in the 5 minutes before they went to sleep. Everyone engaged in a 5 minute writing task in which they recorded what they were thinking. Some were told to suppress thoughts about the person: Try to not think about the crush (or non-crush). Others were told to think about the person and still others simply looked at the name and then thought about whatever they wanted to think about.

In the morning, the participants responded to a dream questionnaire. They recorded the contents of their dreams and rated the extent to which they dreamed about the crush (or non-crush) target person. Wegner and colleagues found a rebound effect: Trying to suppress thoughts about the target person increased dreaming about that person! The rebound worked for both the crush and non-crush target: Emotional connection was not the cause of the dreams. Wegner and his colleagues rebounded their way into people's dreams - Inception, the science.

Trying to not think about something or someone leads to a rebound. You end up thinking about that idea more and you are more likely to dream about the idea or person. Generally the content of dreams reflects the contents of your daily experiences. What Wegner and his colleagues have shown is that trying to suppress thoughts is ironically a powerful method of having the thoughts stick around. You can invade someone else dreams tonight - just tell them to not think about you when they are heading off to dreamland. The rebound effect is a method to control the contents of someone else's dream: Inception works in the movies and in real life.

Inception also makes a point about the difficulty of knowing if something is real or a dream. Once people generate an idea, they may experience trouble tracking the source of the idea. Is this my memory or a suggestion made by someone else (see my post Spilled Punch, Hot Air Balloon Rides, and Enhanced Interrogation)? Did I do that or simply think about doing it? Is this a dream or is this really happening? Tracking the source of our thoughts, memories, and experiences is difficult. Sometimes, we may have a rather tenuous grasp on reality. In the movie, is DiCaprio dreaming or is it real?

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