follow the "M'Naughten test," named for the historically
of the M'Naughten test. (32) The Model Penal Code recommends a
735 (2006), in which the Supreme Court upheld the constitutionality of an Arizona statute that removed the cognitive incapacity element or second prong of the M'Naughten test
. In so doing, the Supreme Court stated that it had never held that the Constitution mandates an insanity defense, but it had also never held that the Constitution does not require such a test.
Texas uses a form of the M'Naughten test. The insanity defense is set forth in Texas Penal Code (TPC) Section 8.01 in two parts: (a) It is an affirmative defense to prosecution that, at the time of the conduct charged, the actor, as a result of severe mental disease or defect, did not know that his conduct was wrong; (b) The term "mental disease or defect" does not include an abnormality manifested by repeated criminal or otherwise antisocial conduct.
The M'Naughten test restricts psychiatric testimony to the narrow scope of a defendant's cognitive capacity and frequently makes it impossible for expert witnesses to describe the complete picture of the defendant's mental illness (TCPOMIa).