Scientists now know that sex hormones begin to exert their influence during development of the fetus. A recent study by Israeli researchers that examined male and female brains found distinct differences in the developing fetus at just 26 weeks of pregnancy. The disparities could be seen when using an ultrasound scanner. The corpus callosum -- the bridge of nerve tissue that connects the right and left sides of the brain -- had a thicker measurement in female fetuses than in male fetuses.
Estrogen and testosterone influence brain development, although the process of the way in which hormones and the brain interact to influence behavior is very complex. Louann Brizendine, MD, author of The Female Brain, points out that gender differences start before birth: female brains are flushed in utero with estrogen hormones, while male brains are washed with testosterone. Females begin studying faces as babies, which shapes their brain development. Research demonstrates that the skills of baby girls in making eye contact and facial gazing increases over 400% in the first three months of life, while facial gazing skills in boys doesn't. In one study, year-old girls looked at their mothers faces 10 to 20 times more than boys checking for signs of approval or disapproval. While the boys, driven by testosterone, moved around the room to investigate their environment and rarely glanced at their mothers.
During puberty, estrogen, progesterone, and testosterone continue influencing development. Teenage girls, flooded with estrogen, get stressed around relationships and ease their fear by banning together and being socially connected. Yes, they can be mean and use their language skills - passive aggressive rumor spreading - to undermine rivals in their competition for the boys (from an evolutionary perspective sexual competition is part of the survival mechanism). But they can apologize and re-bond when necessary. Testosterone flooding the brain of teenage teen boys has the opposite effect: the teenage boy wants to be left alone. He's not interested in conversation because testosterone decreases his desire to socialize except in pursuit of sex or sports. Teenage boys at this time get stressed around challenges to their independence and authority and seek to be respected and find their place in the male pecking order through competition and conflict. They don't look for connection in same way as girls do. These are brain-based behavioral patterns that continue to influence men and women throughout adulthood.
Observations of adult brains show that this area may remain stronger in females. "Females seem to have language functioning in both sides of the brain," says Martha Bridge Denckla, PhD, a research scientist at Kennedy Krieger Institute.
Consider these recent findings. Researchers, using brain imaging technology that captures blood flow to "working" parts of the brain, analyzed how men and women process language. All subjects listened to a novel. When males listened, only the left hemisphere of their brains was activated. The brains of female subjects, however, showed activity on both the left and right hemispheres.
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This activity across both hemispheres of the brain may result in the strong language skills typically displayed by females. "If there's more area dedicated to a set of skills, it follows that the skills will be more refined," says David Geary, PhD, professor of psychological sciences at the University of Missouri.
As a whole, girls outperform boys in the use of language and fine motor skills until puberty, notes Denckla. Boys also fall prey to learning disabilities more frequently than girls. "Clinics see a preponderance of boys with dyslexia," Denckla tells WebMD. ADHD also strikes more boys than girls. The symptoms displayed by girls and boys with ADHD differ, too. Girls with ADHD usually exhibit inattention, while affected boys are prone to lack of impulse control. But not all differences favor girls.
Boys generally demonstrate superiority over female peers in areas of the brain involved in math and geometry. These areas of the brain mature about four years earlier in boys than in girls, according to a recent study that measured brain development in more than 500 children. Researchers concluded that when it comes to math, the brain of a 12-year-old girl resembles that of an 8-year-old boy. Conversely, the same researchers found that areas of the brain involved in language and fine motor skills (such as handwriting) mature about six years earlier in girls than in boys.
So, do these sex differences even out over time?
