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Responsibility & Brain Function

law-order_imageThe idea that behavior is determined by physical causes is hard to reconcile with the intuitive notions of free will and moral agency on which our legal systems are based. Although many people believe that, in principle, human behavior is the physical result of a causally determined chain of biophysical events, most of us also put that aside when making moral judgments. We don't say "but he had no choice--the laws of physics made him do it!"

However, as the neuroscience of decision-making and impulse control begins to offer a more detailed and specific account of the physical processes leading to irresponsible or criminal behavior, the amoral deterministic viewpoint will probably gain a stronger hold on our thinking. Whereas the laws of physics are a little too vague and general to displace the concept of personal responsibility in our minds, our judgment might well be influenced if an offender was shown to have sustained damage to certain brain systems necessary for responsible decision-making and self-control.

What has cognitive neuroscience learned about the causes of "good" versus "bad" behavior? Research has identified brain systems involved in many of the psychological abilities required for prosocial behavior.

The ability to weigh uncertain risks and rewards and make prudent decisions has been intensively studied in simple game-like tasks. Evidence from patients with damage to certain regions of prefrontal cortex and from normal subjects in functional neuroimaging experiments highlights the importance of prefrontal cortex in this ability. Acting without regard to potential negative consequences would be expected to increase the likelihood of criminal behavior.

Other abilities that are essential for prosocial behavior include the ability to take another's viewpoint and to empathize. Brain imaging has shown that when subjects understand stories or cartoon pictures whose plot or punch line depends on the thoughts or viewpoint of a character, some prefrontal cortical and limbic brain regions are more active than during similar tasks in which mental states are not relevant. A network encompassing many of the same areas is active in experiments that evoke empathy or a sense of moral violation.

Furthermore, these brain areas can be damaged in subtle and gradual ways, making it harder to draw a line between someone who should be excused due to an obvious brain injury and someone who should not because their brain is normal. Most illicit drugs affect prefrontal cortex and prolonged use has been linked to impaired prefrontal function. Even childhood abuse or severe neglect, which involve neither a direct mechanical insult to the brain nor a foreign substance crossing the blood-brain barrier, damage these systems. There are also genetic factors that influence the function of these systems.

Society is gradually responding to the emerging neuroscientific view of human behavior. This is evident in our treatment of criminals within the legal system, and also in our social mores and attitudes toward "bad" but noncriminal behavior such as compulsive drinking, gambling or sex. Within the legal system, evidence of neurological dysfunction is frequently introduced in the penalty phases of criminal trials. We perceive this as relevant to the defendant's responsibility for his or her behavior, and it seems reasonable to punish a person less harshly if they are less responsible. This may put us on a slippery slope, however, once we recognize that all behavior is 100% determined by brain function, which is in turn determined by the interplay of genes and experience.

The growing awareness of neuroscience explanations of criminal behavior has prompted ethicists and legal theorists to seek other interpretations of responsibility that do not depend on free will and to propose so-called "forward thinking" penal codes, designed not to mete out just deserts for previous behavior, but to encourage good behavior and protect the public. The "disease model" of substance addiction, and the extension of the medicalized notion of addiction to other compulsive behaviors such as compulsive gambling and compulsive sex, is another way in which brain-based explanations of behavior have impacted society. The disease model emphasizes the deterministic and physiological nature of the behaviors and thereby reduces their moral stigma.

Martha J. Farah

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