Of the super powers one might like to have, mind reading would likely land near the top of the list for many people. Now two papers published this week by Nature Neuroscience show how scientists are inching toward this goal. Magnetic resonance imaging (MRI) scans of people's brains, researchers report, can reveal what types of images they have recently seen.

Yukiyasu Kamitani of ATR Computational Neuroscience Laboratories in Kyoto, Japan, and Frank Tong of Princeton University showed subjects one of eight visual stimuli--images with stripes aligned in various orientations. They determined that the MRI data collected while the volunteers were gazing at the images showed slight differences depending on what picture they viewed. The scientists wrote a computer program that recognized the patterns and found that they could successfully predict what images subjects saw. What is more, when a volunteer was shown two sets of stripes simultaneously--but told to pay attention to just one--the team could tell which set the subject was concentrating on.

In the second experiment, John-Dylan Haynes and Geraint Rees of University College London showed volunteers two images in quick succession, with the first flashing so quickly that the subjects couldn't clearly identify it. But by analyzing their brain activity, the scientists successfully identified which image had been shown, even when the subjects themselves didn't remember seeing it. Together, the results elucidate how the brain reacts to stimuli, even when they are "invisible." If scientists could gain a true understanding of the neural basis of subjective experience, Kamitani and Tong write, it might one day "allow for reliable prediction of a person's mental state based solely on measurements of his or her brain state."