Scientists say they have found a way to get a glimpse of people's dreams.
"Our results show that we can predict what a person's seeing during dreams," says Yukiyasu Kamitani, a researcher at the ATR Computational Neuroscience Laboratories in Kyoto, Japan.
Philosophers, poets and psychologists have long shared a fascination with dreams. But Jack Gallant, a neuroscientist at the University of California, Berkeley says solving the mystery of our dreams is one tough problem.
"In psychology and neuroscience there's been 100 years of argument about whether dreams are important or unimportant," says Jack Gallant, a neuroscientist at the University of California, Berkeley. "We don't really know, because we haven't had very good access to peoples' dreams."
Scientists don't have very good access, because they have to rely on how people talk about their dreams, often as those images are already slipping away.
"Because of the nature of dreams we find it very difficult to remember our dreams and to sort of describe them well," Gallant says. "So the idea is you could perhaps build a dream decoder that would allow you to inspect your dreams after you had them and sort of interrogate them and figure out what you were dreaming about."
Now Kamitani and his colleagues have come up with a decoding program that analyzes brain activity while people sleep.
To do it, Kamitani's team repeatedly scanned the brains of three volunteers just as they were starting to drift into dreams. "We focused on dream experience which can be detected just a few minutes after the sleep onset," Kamitani says.
The researchers awakened the study subjects more than 200 times to ask them to describe their dreams in detail so they could gather data on which patterns of brain activity meant what.
"Many of them were just about daily life in the office," Kamitani says. Others were bizarre or humorous, he says. One man dreamed he was having dinner with a famous Japanese movie star.
The scientists then did more brain scans while the volunteers were awake so they could tweak their program to characterize various patterns of brain activity. "We used that to train the decoder," Kamitani says.
In a paper being published in this week's issue of the journal Science, the researchers then showed they could often predict at least parts of what the subjects were dreaming.
"The results suggest that it may be possible to read out dream contents even when you don't remember just by looking at brain activity," Kamitani says.
Other scientists called the research a technological tour de force, and potentially a milestone toward starting to understand our dreams.
"In this field of dream decoding no one has managed to successfully do this before," Gallant says. "So this is not the final step down this road, it's the first step."
The ultimate goal would be a tool that could provide vivid, detailed representations of our dreams.
"If you could build the perfect dream decoder it would create a movie on your television screen and it would just replay your dreams," Gallant says. "It would replay all the actions that happened, the actors, the people involved and it would replay the sound."
We're nowhere near that yet. But the research reported in Science represents at least a small step toward revealing what we dream and perhaps someday why.