This column discusses problems with use of evidence based on functional brain scans. It describes a 2007 case in which evidence from positron emission tomography of the defendant's brain was used in an attempt to show that he was unable to have planned the sexual assault, which he did not contest committing, and so could not form an intent to commit the crime. Among the issues evident in such cases are the assumption that complex functions are localized to single areas of the brain and the large discrepancy between inferences that can be drawn from such evidence and legal standards that must be met in court.