Surprisingly, these studies were conducted exclusively in women."
Toronto, Aug 12 - Increasing the levels of male hormone testosterone can have a profound effect on our brain's response to threat.
To unravel this, researchers recruited 16 young male volunteers who received either testosterone or placebo.
They focused their attention on brain structures that mediate threat processing and aggressive behaviour including the amygdala, hypothalamus and periaqueductal gray.
The analyses revealed that testosterone increased reactivity of the amygdala, hypothalamus and periaqueductal grey when viewing angry facial 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 Justin Carre, an assistant professor at Nipissing University in Canada.
Understanding testosterone's effects on the brain activity patterns associated with threat and aggression may help scientists better understand the fight or flight response in males that may be relevant to aggression and anxiety.
Expanding our knowledge of exactly how testosterone affects the male brain is particularly important, as testosterone augmentation has become increasingly promoted and aggressively marketed as a solution to reduced virility in ageing men.
Further work is indeed continuing, Carre said.
Our current work is examining the extent to which a single administration of testosterone influences aggressive and competitive behaviour in men, he added.
Prior studies found that the administration of a single dose of testosterone influenced brain circuit function.
Surprisingly, these studies were conducted exclusively in women.
The paper appeared in the journal Biological Psychiatry.