A scan of brain activity can effectively read a person's mind, researchers said.
British scientists from University College London found they could differentiate brain activity linked to different memories and thereby identify thought patterns by using functional magnetic resonance imaging (fMRI).
The evidence suggests researchers can tell which memory of a past event a person is recalling from the pattern of their brain activity alone.
"We've been able to look at brain activity for a specific episodic memory -- to look at actual memory traces," said senior author of the study, Eleanor Maguire.
"We found that our memories are definitely represented in the hippocampus. Now that we've seen where they are, we have an opportunity to understand how memories are stored and how they may change through time."
The results, reported in the March 11 online edition of Current Biology, follow an earlier discovery by the same team that they could tell where a person was standing within a virtual reality room in the same way.
The researchers say the new results move this line of research along because episodic memories -- recollections of everyday events -- are expected to be more complex, and thus more difficult to crack than spatial memory.
In the study, Maguire and her colleagues Martin Chadwick, Demis Hassabis, and Nikolaus Weiskopf showed 10 people each three very short films before brain scanning. Each movie featured a different actress and a fairly similar everyday scenario.
The researchers scanned the participants' brains while the participants were asked to recall each of the films. The researchers then ran the imaging data through a computer algorithm designed to identify patterns in the brain activity associated with memories for each of the films.
Finally, they showed that those patterns could be identified to accurately predict which film a given person was thinking about when he or she was scanned.
The results imply that the traces of episodic memories are found in the brain, and are identifiable, even over many re-activations, the researchers said.
The results reinforce the findings of a 2008 US study that showed similar scans can determine what images people are seeing based on brain activity.