14 DAY TRIAL // It's a fact that women's brains are slightly different from the men's. The difference is not big enough to induce a higher IQ in men or women. But it seems to be significant when it comes to memory, arousal, reasoning, and risk of some diseases, like depression, anxiety, schizophrenia, drug abuse, Alzheimer's, diabetes, and heart disease.
"Brain differences, though small, help us to understand the nature of sex differences in disease, and thus will hopefully aid in devising sex-specific treatments and prevention strategies," observed Jill Goldstein, a professor of psychiatry and medicine at Harvard Medical School (HMS).
Men can use a baby aspirin daily to protect them against heart failure, but Julie Buring, a Harvard professor of medicine who works at the Brigham and Women's Hospital in Boston, discovered that aspirin does not induce the same effect in women.
Alzheimer's disease incidence is higher in women, and this is not linked to the higher longevity in women. They are also more prone than men to type 1 diabetes, rheumatoid arthritis, lupus, and other diseases induced by metabolic or immune impairment. Premenopausal women recover from stroke more quickly and with less damages than men of the same age or postmenopausal women do.
Goldstein's team has discovered a number of brain areas that differ significantly in size between men and women. This could explain sex differences in functions and behavior, like memory and emotionality.
For example, part of the hippocampus and nuclei at the front of the brain, linked to short-term memory, are bigger in the case of women. Other brain regions, linked to mating and arousal, grow larger in males. Do they correlate with an enhanced function in one of the sexes? "This is not always the case. Size alone does not drive function." said Goldstein.
Short-term memory tests made by the research team revealed that although the brain's activity differs between sexes, their short-term memory capacity is matched. "Such results show that male and female brains can take different actions to arrive at the same behavioral response," signaled Goldstein. But these variations can explain slight advantages that women have in verbal fluency and speed of perception. Research data indicate that there is a higher variability in the size of brain nuclei and behavior within each sex than between the sexes. "The great value in exploring this variability is to understand the role that these differences play in certain diseases," Goldstein explains.
This research also points that specific behaviors are not driven just by one brain area. "No single brain region controls a particular behavior. The hippocampus is important in memory but other brain regions are involved. Most functions are regulated by a network of brain regions." said Goldstein.
Hormones and genetic variability seems to lead these sex differences in human brains from the womb to adulthood. Goldstein's team checked the sex differences in response to stress. They scanned women brain while the women watched pictures presenting both neutral scenes, like cows grazing in a pasture, and those that induce emotions, like horrible car crashes. The women were investigated at the beginning of their menstrual cycles and again at ovulation.
Stress nuclei were more stimulated at the beginning of the cycle than during ovulation, but, surprisingly, the women did not display mood change. Male brains reacted similarly to those of women at the beginning of the cycle. The researchers will check which hormones, like estrogen and progesterone, are linked with the differences.
"This is only one of many studies to identify the role of hormones and genes in regulating sex differences in response to stress. We hope that these findings help us understand the higher rates of depression and anxiety in women than in men." said Goldstein.
These investigations could also explain the decreased sensitivity to trauma in men with depression and anxiety disorders, pointing towards sex-specific treatments for mental disorders. The natural decrease in anxiety during ovulation could increase a woman's receptivity, and desire to mate at this right moment. "That idea goes beyond what our data shows us, but it's reasonable to think it may be adaptive for survival of the species." said Goldstein.
The brain's stress response network has been involved also in other mental disorders, like psychosis (when a person loses contact with reality), but also heart disease and diabetes.