What if you could tell what someone was thinking, or better yet, pluck their memories and examine them?  That concept has been fodder for countless science fiction works, and in essence is the goal of lie detection machines.  Unfortunately, to date, lie detection machines and other techniques are crude and error prone at analyzing memories or thoughts.  Additionally, the actual mechanism for memory in the brain is poorly understood.

The field of functional magnetic resonance imaging (fMRI) may change that.  Researchers have made a number of breakthroughs in using fMRI scans to capture brain activity and match it to pre-cataloged images.  

Now researchers have used fMRIs to gain a glimpse of recalled short term human memories and even begin to predict what memory corresponds to what event.  

The new study led by Eleanor Maguire of the Wellcome Trust Centre for Neuroimaging, located in the UK, built on three pivotal previous studies.  The first was previous work, which was performed by Maguire's team, which showed that patterns of electrical activity in the hippocampus could be used to predict someone's position in a virtual world.  The second study was performed at Vanderbilt University and showed that activity in the visual cortex could be used to identify and provide analysis of short-term "working" memory.  The final study came from Japanese researchers, which showed that visual images of memories or sights could be reconstructed, including novel ones that the people had never seen before.

In the new work, Maguire showed 10 participants three short film clips of a woman performing some sort of action.  The clips were shown 15 times and then the participants were sent in for fMRI scanning.  During each scan, the participants were prompted to recall a particular clip in as much detail as possible.  After that, the participants were challenged to a "free recall", in which they decided a particular clip and though about it, afterwards entering what clip they had recalled.  Each participant did 30 such "free recall" trials.

The results were impressive.  All of the participants had the same regions of the hippocampi and hippocampus activated during the act of remembering.  The researchers also showed that during the set recalls, the brain activity (visualized as a "frequency heat map") stayed remarkably consistent.  And during the free recall, they showed that they could correctly predict which clip the participants had selected nearly every time.

The study was published in the journal Current Biology.

It is significant as it establishes what parts of the brain are used for episodic short term memory.  Combined with other studies on spatial short term memory, researchers are approaching being able to "read peoples' minds" for short term thoughts.

Long term memory remains a more elusive challenge, though.  It is thought that experiences cause changes in the frontal cortex, which amount to stored memories.  These memories can be recalled at a much later date, even years after the event.  It is unclear, though, exactly how this works.  Thus we can be thankful that we still have some time before thought crimes like those of Minority Report or other mental snooping could fully be realized.