Art. 46C.051. NOTICE OF INTENT TO RAISE INSANITY DEFENSE. In an insanity defense, the defendant admits the action but asserts a lack of culpability based on mental illness.A defendant who intends to assert a defense of insanity at the time of the alleged offense must so notify an attorney for the government in writing. What Is the Rule of Insanity in Texas? Insanity defenses argue that the person was in a poor mental health state, so they didn't know that what they did was wrong. Notice of an Insanity Defense; Mental Examination. A criminal defendant must meet the jurisdiction's definition of legal insanity for a court to find them not guilty because of insanity. 49 counties in 9 states, PTSD was the basis of an insanity plea in only 0.3 percent of cases. To successfully assert an insanity defense in Texas, certain legal criteria must be met.