Last updated at 11:06 06 March 2008

Scientists have developed a mind-reading technique which could one day allow them to take pictures of memories and dreams.

By comparing brain activity scans, they were able to correctly predict which of 120 pictures someone was focusing on in 90 per cent of cases.

The technique could one day form the basis of a machine to project the imagination on to a screen.

Professor Jack Gallant led the Californian research team.

Writing in the journal Nature, he said: "It may soon be possible to reconstruct a picture of a person's visual experience from measurements of brain activity alone.

"Imagine a general brainreading device that could reconstruct a picture of a person's visual experience at any moment in time."

Two scientists volunteered to look at 1,750 images while data was recorded from their brains and linked mathematically to the "points" that make up a 3D thought image.

This link between brain activity and image was then used to identify which images were seen by each volunteer from a new set of 120, just by looking at their brain scans.

The research evokes sci-fi film Minority Report, where police in the future read people's minds and arrest them for "thought crimes".

But such a situation is a long way off, as the technique currently only works on viewed images, not imagined ones, and it takes hours for the scanners to take the brain images.

Professor Gallant said: "It is possible that decoding brain activity could have serious ethical and privacy implications in 30 to 50 years.

"We believe strongly that no one should be subjected to any form of brain-reading involuntarily, covertly, or without complete informed consent."