It sounds like science fiction: while volunteers watched movie clips, a scanner watched their brains. And from their brain activity, a computer made rough reconstructions of what they viewed.

Scientists reported that result Thursday in the US and speculated such an approach might be able to reveal dreams and hallucinations someday.

In the future, it might help stroke victims or others who have no other way to communicate, said Jack Gallant, a neuroscientist at the University of California, Berkeley, and co-author of the paper.

He believes such a technique could eventually reconstruct a dream or other made-up mental movie well enough to be recognisable. But the experiment dealt with scenes being viewed through the eyes at the time of scanning, and it's not clear how much of the approach would apply to scenes generated by the brain instead, he said.