The Truth Behind Women's Brains PART 3

[Juan and Yenan]

The Truth Behind Women's Brains
20/20's Elizabeth Vargas Looks at the Chemical Changes That Occur Through Life That Change How Men and Women Think

When it was time for the girls to ask a question, Heidi, one of the teens in the class asked, "Why are guys able to like express everything sexually but not emotionally? Like, they can be like, 'Hey baby, what's up?' but, like, they can't, like, say, 'I'm sad.'"

Her classmate Chris Chun offered an explanation: "Guys aren't supposed to feel 'Oh, I feel sad cause my girl broke up with me.' And I think that's what sucks, is that we're expected to keep our feelings inside, and not have any."

A recent neuro-imaging study confirms that the average male, when tracking emotional expressions in the face of another, has fewer brain cells that light up than females do. Men are simply less equipped to read emotion.


Chemistry Does Not Conquer All
Dr. Brizendine insists that despite the "hard wiring" of our brain chemistry, we do have free will. Clearly, not all women and men are the same. But for many the science is undeniable: powerful hormones and the complex circuitry of the brain do shape our behavior and, therefore, our destiny.

"It's biology, and it needs hands-on parenting,'" urged Dr. Brizendine. "It needs 'hands-on parenting.' That's why teens need a lot of wisdom and careful monitoring by adults in order to let the good connections grow strong and get rid of the bad connections."

And becoming a parent also sets in motion dramatic changes in the female mind.

During pregnancy, the biggest hormonal surge of a mother's life will send levels of estrogen and progesterone off the charts. It's something Sarah Cheyette, a pediatric neurologist and mother of three, knows all too well.

"If I'm crying hysterically about something during pregnancy, I feel, 'OK, it's the hormones and I'm not losing my mind entirely,'" said Cheyette.

"The progesterone level goes up -- way up," said Dr. Brizendine. "Thirty, 40 times what is normal… All of the surges and big changes that happen just wire you up for paying attention to that helpless little infant somehow."

During pregnancy, these powerful hormones literally hijack a mother's brain circuits. She first becomes sleepy, hungry and nauseous. Soon, the hormones oxytocin and prolactin intensely focus her maternal brain on the safety, and the needs of her child often to the detriment of everything else.

Scientists don't know why, but neuro-imaging studies show that pregnant women's brains actually shrink -- almost 8 percent -- during gestation. They return to their normal sizes six months after the mother gives birth, and then maternal aggression kicks in. Triggered by hormones, a mother's brain becomes a virtual GPS systems for tracking and protecting her young.