Dr. Brizendine says that in the womb, every fetus starts with a female brain. "In fetal life, at eight weeks of gestation, the tiny testicles in the male start to pump out huge amounts of testosterone that then marinate the brain, changing it into the male brain," she says. "By the time we're all born, we either have a male brain or a female brain."
In a mature woman's brain, Dr. Brizendine says the hippocampus—or memory center—is larger than in the male brain. This area helps people remember emotional event details. "For example, women may remember all kinds of fights they had with their husband that he may not even remember happened at all," she says.
The anterior cingulate cortex is also larger in the female brain. Dr. Brizendine calls this part of the brain the "worrywort" center. "This may be one reason that men don't worry as much as women do," she says.