An age old question is being addressed using modern techniques. When an individual lies, are there detectable differences in their behavior? Or in this case, are there detectable differences in their brain activity? (Yes, you need to have an MRI machine handy). Well, it all depends. Brain activity does change when people lie, but this happens when the person being interrogated believes that technology can be used to detect deception (similar to what happens during a polygraph test). In real life, like when you cannot place your spouse in an MRI machine and ask them questions, detecting deception is extremely difficult to do (see,detecting deception).