Shifty eyes could signal memories that people can't consciously recall: study finds movements linked to activity in hippocampus.

Eyewitness testimony is notoriously flaky, but new research suggests that eye movements can accurately reveal what a person remembers, even if the person isn't aware of the memory.

In a memory test, participants' eye movements picked the right answer even when the participant failed to, Deborah Hannula and Charan Ranganath, both of the University of California, Davis, report in the Sept. 10 Neuron. The eye movements corresponded to activity in the hippocarnpus, a learning and memory center in the brain, suggesting that eye movements can reveal unconscious memories activated in the hippocampus.

Hannula and Ranganath used functional MRI to track the brain activity of volunteers while the participants viewed pictures of faces paired with outdoor scenes. After presenting about 50 such pairs, the researchers showed a landscape picture followed by three faces. Participants were then asked to choose which face had previously been matched with the landscape scene.

When a landscape was shown, activity in the hippocampus increased, followed 500 to 750 milliseconds later by eye movements directed toward one of the three faces. The eyes lingered on the correct face when the hippocampus was more active. Less activity occurred when eyes dwelled on an incorrect face.

Even when participants' responses were ultimately incorrect, the hippocampus activity accurately predicted whether the eyes focused on the correct face. Even if you don't remember learning a relationship between objects, "your hippocampus and eyes might have some of that information left over," Ranganath says.

Communication between the hippocampus and the prefrontal cortex--the brain's executive control region-was reduced when volunteers made the wrong choice compared with trials in which they made the right choice. That result could mean that the hippocampus and prefrontal cortex must communicate properly for a person to remember correctly.

It's still an open question whether the volunteers were conscious of the right choice at the time their eyes lingered on the correct face, Dharshan Kumaran and Anthony Wagner, both of Stanford University, write in a commentary in the same issue of Neuron. The volunteers may have been immediately aware of the right choice but then second-guessed themselves. "There are undoubtedly instances in which first impressions will lead to the correct answer," Wagner says. "When we linger on the choices we sometimes get tricked."