Childhood Trauma Directly Linked to Adult Aggression

Pam Harrison

January 17, 2013

Stressful experiences in early life are associated with higher rates of increased long-term aggression, a new animal study suggests.

Investigators from the Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland, found that male rats that were submitted to fear-inducing experiences during the peripubertal period exhibited high and sustained rates of increased aggression in adulthood, even against unthreatening rodents.

Peripubertally-stressed rats also showed hyperactivity in the amygdala, a region of the brain involved in emotional reaction.

In contrast, the same rats exhibited little activation in the orbitofrontal cortex.

Previous research examining the brains of violent individuals has shown the same deficit in orbitofrontal activation and the same corresponding reduced inhibition of aggressive impulses.

"In a challenging social situation, the orbitofrontal cortex of a healthy individual is activated in order to inhibit aggressive impulses and to maintain normal interactions," states Carmen Sandi, PhD, head of the EPFL's Laboratory of Behavioral Genetics, in a release.

"But in the rats we studied, we noticed that there was very little activation of the orbitofrontal cortex. This, in turn, reduces their ability to moderate negative impulses."

The study was published online January 15 in Translational Psychiatry.

Consequences of Abuse

It is known that violent adults often have a history of childhood trauma, but a direct link between early trauma and neurologic changes has not been demonstrated before.

Using a protocol researchers had developed in their own laboratory, 43 rats were repeatedly exposed to fear-inducing procedures during a developmental period resembling the interval between childhood and puberty in humans.

This period was specifically chosen because it is a time when significant maturational processes occur in regions of the brain important for emotion and cognition.

When the rats reached adulthood, researchers investigated brain activity along with brain region–specific changes in the expression of the MAOA and 5HTT genes, variants of which genetically predispose humans to aggressive behaviors.

"We found that the level of MAOA gene expression increased in the prefrontal cortex," said Dr. Sandi.

Alterations in gene expression were also linked to epigenetic change — in other words, exposure to fear-inducing procedures during the peripubertal period caused long-term modification of expression of the MAOA gene.

The study group also found that treating the same peripubertally-stressed rats with an MAOA inhibitor in adulthood reversed stress-induced antisocial behaviors.

"This research shows that people exposed to trauma in childhood don't only suffer psychologically but their brain also gets altered," said Dr. Sandi.

"This adds an additional dimension to the consequences of abuse and obviously has scientific, therapeutic, and social implications."

The authors have disclosed no relevant financial relationships.

Transl Psychiatry. Published online January 15, 2013. Full article