Brain regions responsible for understanding feelings and emotions show little activity in men when facing anger, which explains their stoic silence in stressful situations.
The study by USC researchers revealed that in contrast, stressed women show increased brain coordination when looking at angry faces.
Advertisement"These are the first findings to indicate that sex differences in the effects of stress on social behaviour extend to one of the most basic social transactions - processing someone else's facial expression," said Mara Mather, director of the Emotion and Cognition Lab at USC.
In the study, the researchers present a series of tests indicating that, under acute stress, men had less brain response to facial expressions, in particular, fear and anger.
In both men and women, looking at pictures of faces caused activity in the part of the brain used in basic visual processing (the "fusiform face area") and in parts of the brain used for interpreting and understanding facial expressions.
However, men under acute stress showed decreased activity not only in the fusiform face area but also decreased coordination among parts of the brain that help us interpret what emotions these faces are conveying.
In a marked sex difference, women under stress showed the opposite - women under stress had increased activity in the fusiform face area and increased coordination among the regions of the brain used in interpreting facial emotions compared to the control group.
Cortisol levels, a known indication of stress, were manipulated using the cold pressor stress test, with no significant sex differences in baseline cortisol or degree of cortisol change.
Men and women under stress were as adept as those in the control group at remembering the faces.
"The study indicates that experiencing acute stress can affect subsequent activity and interactions in brain regions in opposite ways for males and females," said Mather.
"Under stress, men tend to withdraw socially while women seek emotional support," added Mather.
The study has been published in the latest issue of the journal NeuroReport.