As a favor to friends in my academic department, I have frequently been a guinea pig in the functional magnetic resonance imaging (fMRI) scanner. In most of these cases, I fight valiantly against slumber as the stimuli flash on the small screen in front of me and the hypnotic, high-pitched beeps of the scanner reverberate all around. This time, though, it was different. Martin Monti, a fellow neuroscientist at the MRC Cognition and Brain Sciences Unit in Cambridge, England, was going to read my mind. As the bed I lay on slid robotically into the giant doughnut-shaped scanner, I had a strange sensation that I was about to be seen naked—mentally, at least.
The task was simple: Monti would ask me questions—did I have any siblings, did I think England was going to win the soccer match that night, and so on. If I wanted to answer “yes,” then I would imagine myself playing tennis, activating a known set of motor regions in my brain by doing so. If I wanted to answer “no,” then I was to imagine navigating around the rooms of my home, activating an entirely different set of areas involved in scene perception. Given that each scan—and thus each of my yes or no answers—took five minutes, the conversation was not the most riveting I had ever had, but when Monti accurately guessed my response every time, it was nonetheless thrilling and unnerving in equal measure.