The legal system presupposes that we are rational, that we can form mental states and appropriately act on them. But not only must we act appropriately, we must recognize and act upon good reasons. When, in a court of law, we are called upon to explain our actions, it is assumed that we were conscious of our reasons for acting the way we did. The court is reliant on reasoned testimony to do its work. We are expected to explain why we chose certain actions and these explanations are evaluated against what the court believes a rational agent would do. This might appear to privilege consciousness: in cases where the agent is thought to be unaware of their actions, the court usually determines that culpability is diminished. For example, in cases of legal insanity, the court will not convict because they believe the agent was “laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong.” Though this is the legal precedent for an insanity defense, there is something peculiar about this understanding of insanity, for many who claim the insanity defense have a very vivid memory of what they did. They typically give very detailed and internally consistent explanations for their actions. They seem to be very rational—yet no one would want to call them “sane.”

Psychopath and serial killer John Wayne Gacy

William Hirstein and Katrina Sifferd are two scholars who have embarked on a project to understand how the courts understand culpability. They explain that when laws or legal principles appeal to mental states like intentions, knowledge, and purposes, these principles are directed at prefrontal executive processes, brain processes responsible for regulating other, lower-order processes. Executive processes are the control centers of our brains, the cognitive processes in charge of regulating other less complex cognitive processes. They include such functions as attention, remembering, decision-making, planning, intending, and inhibiting. These are the processes invoked when the brain must develop a new way of behaving in response to an unfamiliar task. Hirstein and Sifferd locate executive processes in the prefrontal lobes, the part of the brain where high-order cognitive function takes place. This includes regions such as the dorsolateral frontal lobes, the ventrolateral frontal lobes, the medial prefrontal lobes, and the orbitofrontal lobes. Their main finding is that the court bases its decisions regarding culpability on the quality of the defendant’s executive function.

Consider successful sleepwalking-murder defenses. Parasomnia is a condition, which most generally is defined by disturbed sleep patterns. Many parasomnias involve failed suppression of the motor cortex, the region of the brain responsible for generating movement. This region is fully inhibited in the neurotypical sleeping agent, preventing muscles from firing despite the complex brain activity that may occur. The effects of parasomnia range from simple muscle twitching or kicking to complex activity resembling waking behavior. Somnambulism, or sleepwalking, is the most complex parasomnia. In these cases, people walk, cook, and sometimes even drive in their sleep. There have been several prominent cases of murder in which it was alleged that the defendant was actually asleep during the crime and therefore was not legally culpable for committing the act.

The first example of the successful use of somnambulism as a defense for murder was the case of Kenneth Parks. One evening Parks, who was under the influence of financial stress, drove 15 miles to the home of his in-laws and brutally murdered them. He later showed up at a nearby police station covered in blood, breaking down while telling the police he thought he killed someone. When his case eventually went to trial, doctors testified that sleep studies indicated he was likely a sleepwalker and it was possible that he was sleepwalking when he committed the murders. His story of the night’s events was consistent with the expert testimony leading the court to acquit him of all charges.

We have evidence that acts committed during sleepwalking lack executive function. Research using electroencephalography (EEG) shows that the sleeping brain undergoes certain patterns of electrical activity that can be distinguished as non-REM and REM sleep. Non-REM sleep occurs during the first half of the sleep cycle and shows the lowest levels of brain activity. During non-REM sleep we tend to exhibit very little, if any, activity in the frontal lobes, the areas that house most executive functions. Activity still occurs in other areas of the brain able to execute complex actions, explaining why sleepwalkers are able to initiate very complex actions during this phase of sleep. It plausible that someone completely lacking executive function could commit complex actions such as murder. Hirstein and Sifferd point out that, in these cases, the courts only evaluate executive function when determining culpability. In the Parks case, the court was aware the murder was very sophisticated. They acknowledged that he had a history of engaging in criminal activity. They even acknowledged he had motive. But the lack of executive function led to an acquittal.

Mental disorders not characterized by executive dysfunction don’t make for a strong defense in a court of law. For example, consider psychopathy, a disorder characterized by shallow emotions and the lack of empathy for others. Recently defense attorneys have started introducing functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) scans as evidence that their clients, suffering from psychopathy, have cognitive deficits much like those of juveniles and the mentally retarded, taken by courts to be paradigm cases of executive dysfunction. Some philosophers agree with this move. The trial of Brian Dugan was one of the first cases that required a court to determine if psychopathy could work as a successful defense. Dugan was tried for the 1983 kidnapping, rape and murder of a 10-year-old girl. Neuroscientist Kent Kiehl presented fMRI evidence showing that Dugan had brain abnormalities that matched that of psychopaths. He scored a 37 out of 40 on the Hare Psychopathy Checklist, placing him in the 99.5th percentile. Defense council argued that Dugan’s brain capacity was diminished, a mitigating circumstance in Illinois’ capital punishment statute. Psychopathy is understood to be a disorder of the emotions. They do not perceive other people as valuable because of an emotional deficit. The defense didn’t work; the court swiftly sentenced him to death. Although psychopaths have cognitive deficits, these deficits do not appear to fall into the class of deficits the courts are sensitive to.

But this is one concern: that an exclusive focus on executive function will lead the court to ignore pathology that should mitigate moral culpability that is not believed to fall under the class of executive dysfunction. Take, for example, the case of Charles Whitman. In 1966 he climbed to the top of the University of Texas at Austin Tower and started shooting, managing to kill 16 people and wound 32 others before being killed by police. In his suicide note, later released to the public, Whitman described having recurrent unusual and irrational thoughts: that a tremendous mental effort was necessary to concentrate on normal tasks. He also explained that he decided to kill his wife without any specific reason for doing so. He asked that an autopsy be performed because he was worried something had changed his brain. The autopsy that followed indeed showed that a nickel-sized tumor located on the hypothalamus had impinged upon the amygdala.

The amygdala is part of the limbic system, an evolutionarily old area of the brain involved in emotional regulation. Traditionally, it has not been thought to house executive processes like the more complex cortices do. However, a recent study suggests the amygdala is, in fact, responsible for some executive function. Cordelia Fine et al. (2001) report on a patient, BM, with congenital left amygdala damage. By adulthood, the patient was diagnosed with schizophrenia and Asperger’s syndrome, two mental conditions thought to impair the ability for the agent to form a consistent theory of mind. BM was found to be severely impaired in his ability to represent mental states but a series of tests showed his traditional executive functions, were completely intact. The researchers concluded that because the amygdala is not supposed to be responsible for executive function but appears to influence decision-making, the two must be dissociated. However, there is an alternative explanation: the amygdala appears to have some executive function. Another study shows that the amygdala contributes to decision-making and action planning. It certainly seems that way according to studies showing that damage to the amygdala can result in inappropriate responses in emotional situations.

This suggests a connection between psychopathy and executive dysfunction. Psychopaths seem to be able to morally reason but do not implement it due to a lack of emotional drive. The well-known “trolley” thought experiment asks subjects to make a decision between intentionally killing one person to save five or allowing the five to die but not killing the one person. People with ventromedial damage tend to answer in a way that shows an inability to act with concern for others. A recent study found psychopathic children have reduced ventromedial and amygdala activity, suggesting that these areas play a role in the disorder. This may either be due to congenital defect or averse conditioning, meaning that these defects might be genetic or conditional. A picture starts to emerge: psychopathy appears to fall under the class of executive dysfunction. If this lack of emotional drive is pathological, it is unclear why the court is insensitive to it.

But perhaps disorders like psychopathy truly do not fall under the class of executive dysfunction. Maybe they instead make up the content of executive functions, providing some of the input in decision-making. The concern remains, for the content presumably influences or restricts the nature of the agent’s choices. And these cases the content is defective. There is something intuitively disturbing about punishing a child for her decision when her psychopathy strongly influenced her to choose the wrong one. Non-executive function does matter—it alters the content that is the object of executive function. The court must therefore be sensitive to this underlying neurology when determining culpability.  

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