Barriers to reasonable behavior

The connection between human behavior and body chemistry is well-studied in labs, and sometimes makes its case in courts, as well.


     "Doers" of impulsive crimes show no regard for the consequences. Rather, they are more or less "pushed" by factors beyond their reasonable control. Last month's article in Law Enforcement Technology titled "The brain's hidden agenda" (Vol. 36, No. 5, Page 34) talked about how brain growths and lesions can sometimes inhibit frontal lobe function, resulting in impulsive — and sometimes seemingly unlikely — crimes. Defendants in the case of 65-year-old Herbert Weinstein, an ad executive who was sentenced for the sudden, gruesome murder of his wife, argued Weinstein's behavior could be explained by the fluid-filled arachnoid cyst which surrounded his brain and impaired his reasoning.

     In other cases it's not a cyst or lesion under scrutiny, but a specific gene type or substance that is said to have a similar effect on the brain — perhaps enough to push someone over the edge.

     Neuroscientific studies look into these possibilities and unlock complex yet fascinating questions about the human psyche and the nonfunctioning brain. After all, the more we understand what causes violence, the better equipped we may be to avert it in the first place.

The 'warrior' gene

     Violent tendencies most often stem from a mixture of biological, social and environmental exposures. Digging to the root of the cause, and going at it from all angles, begins in the body itself. A few years back, Dr. Daniel Weinberger of the US National Institute of Mental Health performed a study which suggested some people who are genetically predisposed to violence have a different brain structure altogether. Specifically, the report highlighted a gene called monoamine oxidase A (MAOA) and linked it to an increase in violent behavior. MAOA, which is carried on the X chromosome, produces an enzyme that mops up stress hormones in the brain.

     The most striking study done regarding the gene happened more than 10 years ago in the Netherlands when Australian nueorgeneticist Professor Peter Schofield performed a study on a Dutch family that was found to have a catastrophic mutation within the MAOA gene. The males in the family who had the mutation notoriously committed arson and rape. Although such a mutation is rare, the study prompted the scientific community to take a closer look. Later tests demonstrated that adult mice with an MAOA deficiency manifested a distinct behavioral syndrome, including enhanced aggression in males.

     The MAOA gene and whether or not it predisposes some to violence is certainly a factor in the abstract, and a source of ongoing research. More commonly, there remain a number of psychiatric causes of violence which are neurochemistry-based, says David Hartman, a forensic neuropsychologist in Chicago, Illinois: Bipolar disorder, paranoia and schizophrenia to name a few.

     "An individual with schizophrenic disorder has a higher incidence of violent behavior than other psychiatric disorders," says Hartman. "People who are paranoid believe that they are being threatened in some way; they'll try to retaliate for the delusional threat — not because of a brain lesion — but because of whatever chemical, electrical wiring makes them paranoid, or [because] schizophrenia tells them it's the only option."

Toxic excuse?

     And while some factors predisposing an individual to violence may be hardwired into their DNA, still others may lurk just beneath the kitchen sink. More and more studies indicate that a number of chemicals can toy with brain processes, sometimes causing violent and aggressive outbursts or impulsiveness. Dr. Robert Heilbronner, director of the Chicago Neuropsychology Group, performs a number of neuropsychological evaluations and consultations in criminal, civil and administrative legal proceedings. Heilbronner recalls the case of a heavy glue sniffer:

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