PHILADELPHIA - According to a study that appears in the current issue of SCAN (Social Cognitive and Affective Neuroscience), researchers at the University of Pennsylvania School of Medicine discuss how men and women differ in their neural responses to psychological stress.
"We found that different parts of the brain activate with different spatial and temporal profiles for men and women when they are faced with performance-related stress," says J.J. Wang, PhD, Assistant Professor or Radiology and Neurology, and lead author of the study.
These findings suggest that stress responses may be fundamentally different in each gender, sometimes characterized as "fight-or-flight" in men and "tend-and-befriend" in women. Evolutionarily, males may have had to confront a stressor either by overcoming or fleeing it, while women may have instead responded by nurturing offspring and affiliating with social groups that maximize the survival of the species in times of adversity. The "fight-or-flight" response is associated with the main stress hormone system that produces cortisol in the human body - the hypothalamic-pituitary-adrenal (HPA) axis.
Thirty-two healthy subjects - 16 females and 16 males - received fMRI (functional Magnetic Resonance Imaging) scans before, during and after they underwent a challenging arithmetic task (serial subtraction of 13 from a 4 digit number), under pressure. To increase the level of stress, the researchers frequently prompted participants for a faster performance and asked them to restart the task if they responded incorrectly. As a low stress control condition, participants were asked to count backward without pressure.
The researchers measured heart rate, cortisol levels (a stress hormone), subjects' perceived stress levels throughout the experiments, and regional cerebral blood flow (CBF), which provides a marker of regional brain function. In men, it was found that stress was associated with increased CBF in the right prefrontal cortex and CBF reduction in the left orbitofrontal cortex. In women, the limbic system - a part of the brain primarily involved in emotion - was activated when they were under stress. Both men and women's brain activation lasted beyond the stress task, but the lasting response in the female brain was stronger. The neural response among the men was associated with higher levels of cortisol, whereas women did not have as much association between brain activation to stress and cortisol changes.
"Women have twice the rate of depression and anxiety disorders compared to men," notes Dr. Wang. "Knowing that women respond to stress by increasing activity in brain regions involved with emotion, and that these changes last longer than in men, may help us begin to explain the gender differences in the incidence of mood disorders."
Additional researchers involved with this study are Marc Korczykowski, Penn; Hengyi Rao, Penn; Yong Fan, Penn; John Pluta, Penn; Ruben Gur, Penn; Bruce McEwen, The Rockefeller University; and John Detre, Penn. This study was conducted at the Center for Functional Neuroimaging at the University of Pennsylvania.
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