Section 17 - Insanity defense(a) AFFIRMATIVE DEFENSE.-It is an affirmative defense to a prosecution under any Federal statute that, at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense.(b) BURDEN OF PROOF.-The defendant has the burden of proving the defense of insanity by clear and convincing evidence.Added Pub. L. 98-473, title II, §402(a), Oct. 12, 1984, 98 Stat. 2057, §20; renumbered §17, Pub. L. 99-646, §34(a), Nov. 10, 1986, 100 Stat. 3599.