Functional magnetic resonance imaging (fMRI) produces images of the human brain at work. These are both beautiful and alluring. This means that it is easy to over-interpret them; and unfortunately the media frequently succeed in doing so. Professor Richard Passingham (Emeritus Professor of Cognitive Neuroscience, Department of Experimental Psychology, Oxford) explains what scans do not show and then illustrates what they can show by asking an everyday question: why it is bad to use a mobile while driving?