1. (a) It is an affirmative defense to a prosecution for any crime that, at the time of the commission of the acts constituting the offense, the defendant, as a result of severe mental disease or defect, was unable to appreciate the nature and quality or wrongfulness of his acts. Mental disease or defect does not otherwise constitute a defense.
2. (b) “Severe mental disease or defect” does not include an abnormality manifested only by repeated criminal or otherwise antisocial conduct.
3. (c) The defendant has the burden of proving the defense of insanity by clear and convincing evidence.

(Acts 1977, No. 607, p. 812, §501; Acts 1988, No. 88-654, p. 1051, §2.)