Section 40.15. Mental disease or defect

In  any  prosecution for an offense, it is an affirmative defense that
  when the defendant engaged in the proscribed conduct, he lacked criminal
  responsibility by reason of mental  disease  or  defect.  Such  lack  of
  criminal  responsibility  means  that  at the time of such conduct, as a
  result of mental disease or defect, he lacked  substantial  capacity  to
  know or appreciate either:
    1. The nature and consequences of such conduct; or
    2. That such conduct was wrong.