Neurobiology and Criminal Responsibility: M’Naghten to Elmore

Proceedings of ‏The 2nd World Conference on Social Sciences and Humanities

Year: 2020


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Neurobiology and Criminal Responsibility: M’Naghten to Elmore

Janet Brewer



The first legal pronouncement of insanity in English law dates from the Wild Beast Test of 1723. Just over a century later, this defense was broadened in the case of M’Naghten, articulated by the House of Lords, which continues to shape the American Model Penal Code, a work that plays a critical part in the widespread revision and codification of the substantive criminal law of the United States. But the inherent complexities of defining insanity are compounded by new insights into the workings of the human brain. As the study of neurobiology flourishes, evidence is multiplying that important aspects of behavior can be affected via involuntary exposure to neuro-modulating substances with wide-ranging results–severe psychiatric disturbances to murderous rage.  Since the onset of the medical community’s “Decade of the Brain” in 1990, a new body of scientific literature has emerged with regard to the workings of the brain at the molecular biological level and the role that specific neurotransmitters play in modulating subtle aspects of our behavior.We now know that the brain can malfunction, albeit temporarily, because of conditions over which a person has no control, and that this malfunction can impair the person’s capacity to know what he or she is doing and to remember afterward what he or she has done.  Such knowledge has spawned the defenses of diminished capacity and criminal non-responsibility, offshoots of the insanity defense. This paper explores in what way recent scientific findings may impact criminal non-responsibility.  Part I explains how molecular neurobiology first came to converge with law to become the involuntary neurotoxic damage defense. Part II explores the precise mechanism of action of various neurotransmitters, including acetylcholinesterase, serotonin and others.  Part III examines the influence of molecular neurobiological effects of these neurotransmitters on different aspects of the insanity defense, and the recent U.S. Supreme Court case of Elmore, specifically.

Keywords: Criminal Law, Crime Studies, Legal History.