1. A method for determining whether a subject is truthful or deceptive to a question of interest, wherein it is not known to an examiner beforehand whether the subject is truthful or deceptive to the question of interest, the method comprising the steps of: (a) an examiner asking a subject a question of interest at least twice; (b) the examiner asking the subject at least once to admit to the question of interest during an admission period and at least once to deny to the question of interest during a denial period; (c) measuring brain activity of the subject during each period; (d) comparing brain activity of the subject during the denial period and during the admission period in at least one brain region; (e) optionally repeating steps (a) to (c); and (f) determining when the subject is truthful or deceptive to the question of interest.