- It is an affirmative defense to prosecution 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 or wrongfulness of the defendant’s acts. Mental disease or defect does not otherwise constitute a defense. The defendant has the burden of proving the defense of insanity by clear and convincing evidence.
- As used in this section, “mental disease or defect” does not include any abnormality manifested only by repeated criminal or otherwise antisocial conduct.
- No expert witness may testify as to whether the defendant was or was not insane as set forth in subsection (a). Such ultimate issue is a matter for the trier of fact alone.