Testosterone levels in men have been linked to risks for cardiovascular disease, Parkinson's and even rheumatoid arthritis.testosterone powder

And Medical News Today recently reported on a study focusing on ancient skulls that suggested early humans' breakthrough in tool-making 50,000 years ago coincided with a lowering of testosterone levels in our species.

The researchers from this latest study, led by Justin Carré of Nipissing University in Canada, say previous studies found that administering a single dose of testosterone in subjects influenced brain circuit function, though these studies were - surprisingly - carried out in women.

To investigate testosterone's effects on the brain's threat response in men, the team recruited 16 healthy young male volunteers. Focusing on brain structures involved in threat processing and aggressive behavior, such as the amygdala, hypothalamus and periaqueductal gray, the researchers had the men complete 2 test days during which they received either a placebo or testosterone.

"Understanding testosterone's effects on the brain activity patterns associated with threat and aggression may help us better understand the 'fight or flight' response in males that may be relevant to aggression and anxiety," says Dr. John Krystal, editor of Biological Psychiatry.During the testing days, the men received a drug that suppressed their own testosterone so as to ensure that all study participants had similar levels for the study. As such, any men who received testosterone only received enough to return their levels to the normal range.

Next, the men underwent a functional magnetic resonance imaging (fMRI) scan while completing a face-matching task.