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USA TODAY - Brain scans can reveal the visual images that people see when they sleep, report Japanese researchers on Thursday, in a dream "decoding" study.

The report follows recent advances in decoding the brain signals that correspond with what patients see while they are awake. And it suggests that the brain uses common mental circuits to perceive images whether asleep or awake, say researchers, who are looking at both basic brain function and for ways to treat hallucinations in psychiatric patients.

Is it mind reading? "In the sense that one can gain some information about another person's subjective state, this may be called 'mind reading,' " says study senior scientist Yukiyasu Kamitani of Japan's ATR Computational Laboratories in Kyoto. "But the performance of our current method falls far short of the level people would expect for 'mind reading' in terms of the accuracy and the level of details."

In the study in the journal Science, Kamitani and colleagues asked three people to repeatedly sleep inside "functional" magnetic resonance imaging machines (fMRI), which observe changes in blood flow in the brain. They compared the brain activity the volunteers showed during light sleep to what they exhibited on being shown images of common things, like cars or streets, while awake. They also woke the volunteers to quiz them on what they were seeing while asleep 10 seconds previously, to check on the results. ("Um, what I saw now was like, a place with a street and some houses around it," was a typical response from a volunteer, the study says.)

Overall after 200 awakenings, a computer process could reliably "decode" images the volunteers had seen while asleep roughly 60% of the time. "Our result suggests that during dreaming, parts of the brain work as if they are in wakefulness," says Kamitani, by e-mail.

"These things can be done in wakefulness already. Dreams are just an extension of this brain state, and I don't see why it should not work here," says neuroscientist Michael Czisch of Germany's Max Planck Institute of Psychiatry. In 2011, Czisch and colleagues reported that dreamers clenching their fists asleep in an fMRI machine used the same parts of the brain to do so as they did when awake. Other brain scan researchers have decoded images or objects being observed or pondered by awake people, even re-creating blurry versions of movie clips as they watched them (such as the remake of The Pink Panther, which the University of California-Berkeley researchers watched themselves, an experience "too brutal a procedure to visit on innocent outsiders," as The Economist put it).

The Japanese researchers next hope to extend their efforts to look at the deep "rapid eye movement" portion of sleep associated with deep dreams, which has proven difficult to examine in past studies due to the noise and discomfort of the brain scanning machines. Kamitani suggests that the ethics of decoding mental imagery needs to be discussed as the procedure improves.

"I think in principle it will be possible in the future to catch a dream storyline, but most likely not in the form of a movie which the researcher can follow on a monitor, but more in a sense that certain items and objects can be identified as being part of a dream scenario," Czisch says. However, he thinks mind reading by brain scan is a long way off. "Just by moving a bit all the time, and by singing songs in your head while being scanned may produce sufficient 'brain-noise' to inhibit someone reading your thoughts."