Scientists have created a mind-reading machine that allows them to reconstruct images in a person's mind using brain scans.

They believe that the technology could be used to create e-fits from someone's memory of a crime, or even create pictures of dreams.

"It is a form of mind-reading," Marvin Chun, professor of psychology, cognitive science and neurobiology at Yale University said.

Researchers Chun, Brice Kuhl of New York University and Alan Cowen of the University of California at Berkeley made the astonishing breakthrough.

They built on previous research in which scientists were able to identify whether a person was looking at a beach or city scene, an animal or a building, using brain scans.

"But they can only tell you they are viewing an animal or a building, not what animal or building," Chun said.

"This is a different level of sophistication."

He said that large areas of the human brain are involved in facial recognition, a testament to its evolutionary importance, and this presented a challenge for researchers seeking to map the neural processes.

"We perceive faces in a much greater level of detail than we perceive other things," Cowen said.

The researchers showed six subjects 300 pictures of faces while they were undergoing functional MRI scans. This allowed them to identify how their brains were reacting to seeing different coloured hair, or features of different shapes.

They used the resulting data to build a map of how the brains responded to the faces.

Then, they showed the subjects new pictures of faces while their brains were being scanned, and using only the information gained, compared how the brain was reacting with how it reacted to other face types to make the pictures.

"This methodology not only represents a novel and promising approach for investigating face perception, but also suggests avenues for reconstructing 'offline' visual experiences—including dreams, memories, and imagination—which are chiefly represented in higher-level cortical areas," wrote the team.