09/28/2015 05:20 pm ET Updated Sep 28, 2016

The Insanity of the Insanity Defense

I am a physician, a perinatal psychiatrist working with childbearing women. Although I am not a forensic expert, I have testified in court for mentally ill defendants. In this capacity, I have come to understand that the definition of insanity in psychiatry is not the same as the definition of insanity under the law.

The United States legislature embraces a definition of insanity determined by the 1843 M'Naghton standard, which remains current in the courtrooms of most states in our nation. This 19th century "cognitive" test is used to determine the defendant's capacity to "know right from wrong" at the time of the crime, which is the basis for deciding if someone is "not guilty by reason of insanity (NGRI)".

Approximately 29 countries including the United Kingdom, Australia, and Canada have infanticide laws that recognize the biological vulnerability to psychiatric illness in childbearing women. These mothers are sent to psychiatric hospitals for treatment. In the United States, they are charged with homicide with possible sentences of life in prison or even the death penalty.

The M'Naghton test of "right or wrong" was born out of the English case of Daniel M'Naghton, a man who suffered from paranoid schizophrenia. During his murder trial, Queen Victoria ordered the judges to provide a definition of insanity. The judges wrote, " must be clearly proved that, at the time of committing the act.... that he did not know he was doing what was wrong". Even today, that impromptu definition decides the fate of defendants who seek to be found not guilty because of mental illness.

The arbitrary nature of this law impacted me when I was asked to consult on the retrial of Andrea Yates in 2006. In 2001, during an episode of postpartum psychosis, Mrs. Yates experienced a delusion that Satan was in her presence, and directed her to drown her five children in the bathtub of her Houston, Texas home. Satan declared to Andrea that drowning her children would guide them to heaven and spare them from the burning in hell. Any good mother would save her children from endless pain and suffering.

Before this postpartum psychosis scarred her brain, Andrea Yates had been a good mother, a nurse, a mom who homeschooled her 5 children and taught bible lessons. But, when a person is psychotic, she inhabits an alternate reality, a mental state in which she interprets events differently from others around her. Her reality is that space in time, crowded and confused with delusions, visions and voices meant only for her. So Andrea followed Satan's directions. With this fundamental understanding, she prepared her children for their journey to heaven by placing them in bed according to age-each one's arm around the younger for protection.

When a defendant pleads "insanity" in court, psychiatrists administer the M'Naghton test to determine if the defendant was "insane at the time of the crime." The psychiatric expert inquires, "Mrs. Yates, when you were drowning your children, did you know that what you were doing was wrong?"

This M'Naghton rule begs scientific inquiry. The statute presumes that the subjective reality of the psychotic individual matches our reality. It applies logic to the illogical state of the defendant's "psychosis." Yet, current research has demonstrated that psychotic states are associated with impaired cognition. How can a person whose illness alters her cognitive ability to reason be held to a "cognitive" standard of "right or wrong" when her mind cannot function at this level of reason?

Adding insult to scientific injury, the "Deific Decree" doctrine provides an additional standard for insanity in the courtroom, and lends further support to the mismatch between science and the law. The doctrine was conceived in 1915 by Justice Cordoza in the case of People vs Schmidt (Supreme Court of the State of New York). Cordoza declared "if ... there is an insane delusion that God ... ordained the commission of a crime, ... it cannot be said of the offender that he knows the act to be wrong," Therefore, a defendant directed by God to commit a crime is "not guilty by reason of insanity."

When Deana Laney told a Tyler, Texas court in 2004 that she was commanded by God to stone her children to death, she was found not guilty by reason of insanity and remanded to a psychiatric facility. But in 2001, in the same jurisdiction, with the same psychiatric experts, Andrea Yates whose delusions were directed by Satan was found sane, guilty of capital murder and sentenced to prison for life.

At the time of the 1843 trial of Daniel M'Naghton, bloodletting was the treatment of choice for psychiatric illness. The manuscript, Bloodletting in Mental Disorders was published in the April 1854 volume of the American Journal of Insanity (the former American Journal of Psychiatry). Today our therapeutic interventions focus on brain chemistry, neural circuits, and cognitive neuroscience. Psychiatric medications have replaced bloodletting, but M'Naghton endures.

The Deific Decree doctrine begs the question; can we distinguish the insane from the sane by whether the neurochemicals in their brain speak to them through God or Satan? Should we use the 173-year-old M'Naghton rule based on "cognition" if cognitive impairment is fundamental to psychosis? Can 19th C. law meet the standards of 21st C. neuroscience?

In her retrial, where I served as an expert consultant for the defense, Andrea Yates was found "not guilty by reason of insanity," and remanded to a forensic psychiatric facility. Her delusions are now controlled by medication and therapy, but there are none for her pain.

Intelligent and compassionate physicians and legislators owe mentally ill defendants laws based on scientific facts, not antiquated jurisprudence.