Identifying the Root of Male Aggression

Neurologists have recently identified the part of the male brain that is specifically triggered by testosterone to prompt aggressive behavior. The researchers say that this could bring them one step closer to truly understanding aggression and its relationship with the male hormone.

Experts have long suspected that the steroid hormone testosterone could be linked to aggression. While the hormone is present in both men and women, it is seen at significantly higher levels in men, who have also been found to be more susceptible to fits of violent anger.

Now, according to a study published in the journal Biological Psychiatry, researchers have investigated testosterone's effect on the parts of the brain that are involved in threat processing and aggressive behavior - namely the amygdala, hypothalamus, and the periaqueductal gray.

"Understanding testosterone effects on the brain activity patterns associated with threat and aggression may help us to better understand the 'fight or flight' response in males that may be relevant to aggression and anxiety," commented Dr. John Krystal, Editor of Biological Psychiatry.

The study details how, based off previous studies involving women, researchers had 16 healthy male volunteers complete two days of testing. During this time, the subjects were all given either a placebo or testosterone. They were also given a drug that suppressed their own natural testosterone levels to ensure consistent base levels among all the participants.

These men were then asked to complete a face-matching task while they underwent functional magnetic resonance imaging (fMRI).

Interestingly, if somewhat predictably, the participants given elevated levels of testosterone showed increased activity within the aggressive parts of the brain when viewing angry expressions.

"We were able to show for the first time that increasing levels of testosterone within the normal physiological range can have a profound effect on brain circuits that are involved in threat-processing and human aggression," said lead researcher Justin Carré.

That should help pave the way for future work. Carré says his team is now looking at how a single elevation of testosterone can influence competitive behavior in men.