Scientists have identified a gene that may increase the risk for
impulsivity and violence, particularly in men.
The new study adds fuel to the debate over whether nature or
nurture is to blame for criminal and disagreeable behavior.
Researchers tested 142 healthy volunteers, free from psychiatric or
neurological illnesses as well as drug or alcohol abuse, for the
presence of a variation of the gene that produces low amounts of
monoamine oxidase A (MAO-A)a substance that previous studies have
associated with impulsive violence.
People have one of two versions for this geneMAOA-L, which
produces low levels of MAO-A, and the high level version,
MAOA-H.
The researchers also imaged each volunteers brain activity during
a series of tasks, including responding to facial expressions and
emotional scenes.
Volunteers with the MAOA-L gene have lower volume in two brain
structures, the amygdala and cingulated cortex. The amygdala is
associated with fear and anger and the cingulate cortex regulates
the amygdala and helps inhibit behavior.
When viewing frightening scenes or faces perceived as angry, MAOA-L
individuals showed increased amygdala activity and reduced
amygdala-regulating activity.
Men with MAOA-L also showed increased amygdala activity when
recalling negative memories, and had impaired function of the
cingulated cortex when trying to hold back a physical
response.
It is important to note, however, that these individuals are not
destined to become violent criminals, as the individuals in the
study were all considered psychologically normal.
By itself, this gene is likely to contribute only a small amount
of risk in interaction with other genetic and psychosocial
influences; it wont make people violent, said study co-author
Andreas Meyer-Lindenberg of the National Institutes of Health. But
by studying its effects in a large sample of normal people, we were
able to see how this gene variant biases the brain toward
impulsive, aggressive behavior.
The MAOA-L variant is likely just one of many genes that play a
role in controlling impulsive aggression. However this finding
reveals a connection between a persons genetics and environment
when controlling behavior.