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A dose of testosterone increases the brain's response to threat in healthy men, according to a new study.

Previous studies showed that testosterone administration increased brain circuit function in women. Researchers wanted to see if testosterone also increases response to threat cues in male brains.

Lead researcher Dr. Justin Carré, Assistant Professor at Nipissing University, and his team focused on brain structures responsible for threat processing and aggressive behavior. These brain regions include the amygdala, hypothalamus and periaqueductal gray.

 The study involved 16 healthy young men who were asked to compete two days of tests. Participants were given placebos on one test day and testosterone on another day. However, all participants received a drug that suppressed their testosterone on both test days.

The findings revealed that testosterone enhanced reactivity of the amygdala, hypothalamus and periaqueductal grey when participants viewed 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," explained Carré. "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," added Dr. John Krystal, the Editor of Biological Psychiatry, according to a news release.

Researchers said that studying how testosterone influences the male brain is very important because testosterone enhancement products are becoming increasingly popular, especially among aging men suffering reduced virility.

"Our current work is examining the extent to which a single administration of testosterone influences aggressive and competitive behavior in men," Carré concluded.

The findings are published in the journal Biological Psychiatry.