Now accumulating research, which includes human psychological and physical imaging studies, shows that there are indeed subtle brain differences between the sexes.
The research, conducted by female and male scientists, is leading to:
A better understanding of gender.
Possible alterations in the details of certain treatments.
In the late 1960s and early 1970s scientists found the first clear evidence that brain differences exist, in rodents at least. One study showed differences in nerve cell body size in an area of the brain known as the hypothalamus, which is important for feeding, drinking and reproduction. Another examination of areas in the hypothalamus showed that the structure of certain connections differed between male and female rats. These connections, called synapses, are the sites where nerve cells transmit messages. The scientists also found differences in the number of connections.
Since that time, researchers have discovered a number of differences in humans and other species. Many of these findings go beyond reproduction. For example, studies show that human male brains are, on average, approximately 10 percent larger than female brains. Certain brain areas in women, however, contain more nerve cells.
At this point, researchers do not know how the structural differences influence brain function. It's possible that male and female brains work at a similar capacity but process information differently. For example, one study shows that men and women perform equally well in a test that asks subjects to read a list of nonsense words and determine if they rhyme. Yet, imaging results found that women use areas on the right and left sides of the brain, while men only use areas on the left side to complete the test.
Other research suggests that, on average, the female brain performs better on some skills while the male brain executes other tasks at a higher level. For example, tests show that women generally can recall lists of words or paragraphs of text better than men. On the other hand, men usually perform better on tests that require the ability to mentally rotate an image in order to solve a problem. Mental rotation is thought to help people find their way, according to researchers. Does that leave the majority of women lost? Obviously not. Scientists believe that women may rely on their memory advantage and recall landmarks to find a destination.
It makes sense that brains vary between the sexes, according to some researchers. In ancient times, each sex had a very defined role that helped ensure the survival of the species. Cave men hunted. Cave women gathered food near the home and cared for the children. Brain areas may have been sharpened to enable each sex to carry out their job.
Today, the research on brain differences could protect survival by improving treatments for a variety of disorders.
An example of how insights could lead to refined patient care is illustrated by a recent imaging study. The research shows, on average, that women synthesize the chemical serotonin at a lower level than men. Currently serotonin is a popular drug target because it has been implicated in a number of diseases, including depression. Scientists may be able to expand the synthesis finding and develop customized treatments. The research also could help improve the evaluation of therapies.
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