Scientists say they have found a way to "read" people's dreams by using MRI scanners to monitor brain activity.

Three volunteers were woken around 200 times each and asked what images they had seen during the first, light moments of sleep.

Their answers were then matched with the parts of their brain which were active and grouped into broad categories, for example men, words and books.

Volunteers were also asked to look at photos from the internet corresponding to their dream images while their brain was monitored.

The Japanese scientists then found they were able to predict what images the volunteers were seeing with about 60% accuracy.

"We have concluded that we successfully decoded some kinds of dreams with a distinctively high success rate," said Yukiyasu Kamitani, from ATR Computational Neuroscience Laboratories in Kyoto.

"I believe it was a key step towards reading dreams more precisely."

While scientists are still a long way from being able to 'tune in' to the intimate details of dreams, the study could help progress psychological therapy and sleep research.

The "stunning" experiment was "probably the first real demonstration of the brain basis of dream content," said neurologist Dr Robert Stickgold, from Harvard Medical School.

He told the journal Science - which published the study - that researchers had never before been able to predict the content of dreams with such accuracy.

"Up until this moment, there were no grounds on which to say we don't just make up our dreams when we wake up," he added.