Did my brain make me do it?


Our first case is from a 40-year old man who developed a new and intense interest in child pornography.  His sexuality also generally increased, and he found himself frequenting prostitutes even though he never had before.  He was ashamed of his behavior and went to lengths to hide it, and could communicate that it was morally wrong.  However, he then began making sexual advances on his pre-pubescent step-daughter and spoke of raping his landlady.  He was removed from his home, but failed a 12 step sexual addiction program as he could not restrain himself from soliciting sexual favors from the staff and fellow group members.  As he failed the program, he was sentenced to prison, but developed debilitating headaches and balance problems shortly before admission.  An MRI revealed a large tumor in his orbitofrontal lobe, an area associated with self control, executive function and the regulation of social behavior.  Following surgical removal of the tumor, the man was able to successfully complete the sexual addition course, successfully moved back in with his family and no longer had pedophilic or other deviant urges.

Consider, then our second case: the 1992 trial of Herbert Weinstein, a 65-year-old advertising executive who was charged with strangling his wife to death and then, in an effort to make the murder look like a suicide, throwing her body out the window of their Manhattan apartment.  At his neuropsychiatric evaluation, it was found that Mr. Weinstein had a small, subarachnoid cyst in his brain. The defense moved to use this cyst as evidence of Mr. Weinstein’s inability to control, or be responsible for, his behavior. The cyst in Weinstein’s brain has never been linked to mental illness or violent behavior. After a contentious pre-trial hearing about using this evidence, Mr. Weinstein accepted a plea bargain.

Are both of these men equally responsible for their own behavior?

A central tenet of neuroscience is that all behavior is caused by the brain. This sounds simple enough, but given our long intellectual history of separating the mind from brain, we hold very dear to the idea of an “I”, separate from the 3 pounds of electrical meat that is our brain, calling the shots. After all, “I” feel like “I” make decisions that shape my life. If “I” wasn’t responsible for these decisions, if the decisions instead came from the electrical meat, which is determined by the laws of physics, then how is it that “I” decided to wear a blue shirt instead of the red one? More troubling, if “I” am just my brain, and my brain is malfunctioning, am “I” still responsible for my behavior?

People are remarkably consistent in their moral judgments. Therefore, with some confidence, I can predict that you feel that the man from case 1 is less responsible for his behavior than Mr. Weinstein from case 2.  Is this gut-level feeling rational? After all, both men had damage to their brains, and their brains govern their behavior.

The problem with many cases of “my brain made me do it” arguments is that the association between a brain injury and a behavioral problem is not causal evidence that the injury caused the behavior. Another way of saying this is that “correlation does not imply causation”. We are quick to call B.S. on associations that don’t seem to have plausible causal connections: although drowning is associated with ice cream consumption, we do not guess that ice cream causes drowning. In the criminal realm, we are also likely to see through a Twinkie defense, even if “neuro-babble” makes for a more compelling case.

However, in the case of the first man, we are able to establish a causal connection between his brain injury and his bad behavior: he had “normal” behavior (presumably) before and after the tumor. Unfortunately, we cannot surgically repair most malfunctioning brains, so most connections between behavior and brain are speculative.

Beyond the problem of causality is the problem of will. How can we establish that someone absolutely cannot control his behavior? People can exhibit a certain degree of regulation over even autonomic functions using biofeedback or certain styles of meditation. In the lab, feedback from fMRI has been used to train subjects to willfully activate and de-activate a region involved in the perception of pain. However, it is incredibly difficult to willfully change most behaviors. It takes many days of consistent effort to form new habits. Many ex-smokers report that the physical withdrawal from nicotine was much easier to deal with than the reprogramming of one’s automatic response to grab a cigarette in various contexts. Although the politics of how we frame addiction is a larger topic for another post, suffice it to say that there is no consistent agreement what behaviors we expect people to be able to control, and those we don’t.

So, did my brain make me do it? Well, yes, of course it caused my behavior. Am I to be held responsible for this behavior? Given the above difficulties, I have to agree with Michael Gazzaniga who states that this question is to be left to the legal scholar and not the neuroscientist.