The Brain-Disordered Defendant: Neuroscience and Legal Insanity in the Twenty-First Century

Brain-damaged defendants are seen everyday in American courtrooms, and in many cases, their criminal behavior appears to be the product of extremely poor judgment and self-control. Some have a disorder in the frontal lobes, the area of the brain responsible for judgment and impulse control. Yet because defendants suffering from frontal lobe dysfunction usually understand the difference between right and wrong, they are unable to avail themselves of the only insanity defense available in many states, a defense based on the narrow McNaghten test. “Irresistible impulse” (or “control”) tests, on the other hand, provide an insanity defense to those who committed a crime due to their inability to exercise behavioral control. Control tests have fallen into disfavor, however. Opponents of control tests offer three rationales for their abandonment: (1) that cognitive tests for insanity are sufficient, since those with impaired impulse control will also be cognitively impaired; (2) that mental health professionals are incapable of reliably assessing the capacity for impulse control, particularly in relation to criminal behavior, or of differentiating between a truly irresistible impulse and an impulse that is merely difficult to resist; and, therefore, that control tests lead to erroneous insanity acquittals; and, (3) that because “they directly pose the question of whether a person could control his or her behavior,” control tests run counter to the law’s assumption that people have free will and bear responsibility for their actions. Current neuroscience research presents a challenge to these claims. In the Article, I argue for a return to control tests for insanity, but with important doctrinal modifications