According to what I remember from college. The Amigdala controls the flight or flight mechanism. The Hypocampus is the memory center of the brain. I'm not really an expert, but my guess is that they'll be looking for it in either the hypocampus, or else the amigdala. I suppose they could find something in the speech center center of the brain. On discovery channel: A new lie detector test uses an MRI scan. It shows that when a person is lying there is hyperactivity in the speech center of the brain.
So this is probably the application of the MRI Lie Detector test.
If you don't really know but shoot your mouth off anyway, does that make me a liar?
If you don't really know I'm premed with a neuroscience focus; I don't know, but I know enough about MRI to know that it takes a huge cycling magnet and about twenty minutes at least...and I know that the brain is incredibly complex, that neuroscience is in its barest infancy, and that most of what we do with it is so crude as to be either only applicable in very specific circumstances or so gross as to cause massive side effects.
Lie detectors only work because people think they do--if they're not nervous, they detect nothing.