Lying can be detected by various imaging techniques as well as by trained human observers. There is an interesting review article in the Feb. 5, 2006 NYTimes magazine by Robin Marantz Henig "Looking for the Lie". Note these VERY IMPORTANT critical comments of Steve Kosslyn, who has distinguished imaging difference between spontaneous and rehearsed lies:
"Kosslyn remains skeptical about the brain-mapping enterprise as a whole. "If I'm right, and deception turns out to be not just one thing, we need to start pulling the bird apart by its joints and looking at the underlying systems involved," he said. A true understanding of deception requires a fuller knowledge of functions like memory, perception and visual imagery, he said, aspects of neuroscience investigations not directly related to deception at all. In Kosslyn's view, brain mapping and lie detection are two different things. The first is an academic exercise that might reveal some basic information about how the brain works, not only during lying but
also during other high-level tasks; it uses whatever technology is available in the sophisticated
neurophysiology lab. The second is a real-world enterprise, best accomplished not necessarily by using elaborate instruments but by encouraging people "to use their two eyes and brains." Searching for a "lie zone" of the brain as a counterterrorism strategy, he said, is like trying to get to the moon by climbing a tree. It feels as if you're getting somewhere because you're moving higher and higher. But then you get to the top of the tree, and there's nowhere else to go, and the moon is still hundreds of thousands of miles away. Better to have stayed on the ground and really figured out the problem before setting off on a path that looks like progress but is really nothing more than motion. Better, in this case, to discover what deception looks like in the brain by breaking it down into progressively smaller elements, no matter how artificial the setup and how tedious the process, before introducing a lie-detection device that doesn't really get you where you want to go."