Scientists have shown for the first time that it may be possible to "read" a person's mind simply by looking at brain activity.
Using a modern scanner to measure blood flow, British researchers said on Thursday they were able to tell where volunteers were located within a computer-generated virtual reality environment.
"Surprisingly, just by looking at the brain data we could predict exactly where they were," Eleanor Maguire of the Wellcome Trust Center for Neuroimaging at University College London told reporters.
"In other words, we could 'read' their spatial memories."
The discovery opens up the possibility of developing machines to read a range of memories, although Maguire said the risk of "intrusive" mind reading was still a long way off.
Instead, she believes the discovery, reported in the journal Cell Biology, will help research into memory disorders such as Alzheimer's by shedding light on how the hippocampus region of the brain records memories.
Maguire and colleagues used a technology known as functional magnetic resonance imaging, or fMRI, which highlights brain regions as they become active.
By scanning the brains of people as they played a virtual reality computer game they were able to measure the activity of certain neurons in the hippocampus, a region known to be critical for navigation and memory.
The research paves the way for analyzing how other thoughts — including fuller memories of the past or visualizations of the future — are encoded across neurons.
That could eventually mean using fMRI for forensic examination of a whole host of memories and thoughts, opening up a potential ethical can of worms.
For the moment, however, the technology only works with willing volunteers and fellow researcher Demis Hassabis said it would be at least 10 years before forensic applications became a possibility.
"It's a long way off before that kind of technology is going be possible where you can read someone's thoughts in a single short session, when they don't want to be cooperative," he said.