Neuroscience, Law, and “The Christmas Tree Effect”

Medical and legal professionals have for a long time known that damage to the brain can cause a personality change, whereby the individual becomes more aggressive. Antonio Damasio has famously referred to this phenomenon as “acquired sociopathy”, and perhaps the most famous and most parroted case of acquired sociopathy is the life of Phineas Gage. Gage, a nineteenth century railroad worker, had an iron bar used for packing down explosives into rock, explode up and into his head, destroying a good chunk of his frontal lobe. After the incident, Gage was said to have changed – he was suddenly aggressive and unwilling to conform to the moral norms and values of the time (and not in a libertine kind of way).

This phenomenon is still happening today, but not just from accidents resulting in brain injuries, but also from the natural formation of tumors and the required surgery to remove them, and from dementia, such as Alzheimer’s Disease. While there is still no way to causally connect the damage to the resultant antisocial or criminal behavior, there seems little doubt that the the damage did increase the probability of said behavior from close to zero to probable. But how do you account for this probability in a legal setting?

The questions asked by the prosecution are usually driving at “Did they do it?” and “Were they in control when they did it?” The first question seems fairly simple, because somebody had to do have committed the act, but the second question is far from black or white, and probably should not be left up to lay people to decide. If an individual never acted aggressively, then suffered frontal lobe damage and subsequently had a penchant for assaulting strangers, would we still want the full weight of the law to crash down on them?

These PET scans were not used in a criminal court case. I’m just using them to demonstrate how PET scans can just simply dazzle you without really offering any useful information.

The problem from the side of the prosecution with neuroscience defenses is that there is no causal link between brain injury and aggression, and even if there was it doesn’t rule out that the individual had no control whatsoever, despite the injury. That is to say his drive to commit these acts may have increased from a minimal or none existent desire to where he needed to lock himself in a room to prevent going out and hurting anyone. There is no brain scan that can show a level of “self control” or provide a probability of offending. So when functional magnetic resonance imaging (fMRI) or positron emission tomography (PET) is used to show levels of activity in various parts of the brain, the prosecution is likely to dismiss them as “The Christmas Tree Effect” – pretty pictures of the brain that are meant to dazzle and distract the jury.

Neuroscience has come a long way in understanding the neurobiology of crime. We know that poor impulse control, which is associated with many criminal behaviors, can result from abnormal levels of serotonin. We know that the brain of the psychopath has significant differences when compared to the non-psychopath brain. We know that pedophiles, too, have significant differences in their brains. But none of this is ever going to please the prosecution, because they need the guy to have done it; not his different or damaged brain, but him.

In this respect, the prosecution is never going to merit neurobiological explanations of criminal behaviors, because neurobiology pulls the concept of agency apart in a way that they can’t deal with. Neuroscience and prosecutors, it seems, are destined to remain enemies forever.

Copyright Jack Pemment, 2012


Additional Source

Davis, K. (2012) Brain Trials: Neuroscience is taking a stand in the courtroom, ABA Journal, 11/2012

One thought on “Neuroscience, Law, and “The Christmas Tree Effect”

  1. K.P. Dawson

    I think that until neuroscience progresses to the point where all mental defects/injuries can be cured, in the legal setting we will have to continue to assume that someone is in control so long as they meet the standing tests for sanity. Otherwise, where does it end? Do we stop prosecuting murderers and rapists because the neurology made them do it?

    We have to balance the need to protect the majority of society against the need to help those who are perhaps driven to commit criminal acts because of some brain defect. Our current public policy says that protecting people from harm is the greater need.

    But this will change if at some point in the future curing aggressive behavior is as simple as a single surgery. Of course, that opens up a whole new avenue of legal issues: If a sociopath doesn’t want to be cured, do we force it on them?



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