Neurobiologist Dr. Louanne Brizendine studies the difference between female and male human brains, the sort of topic that will always draw an audience’s interest. She explains that she moved from a career in architecture, where she was one of the few females, to work with the feminist movement at Berkeley, where “there was mandatory unisex clothing and mandatory unisex brains.” She offers some context for why people could believe in the unisex brain, which was an unwillingness to study female brains. A prominent pyschologist told her that he wasn’t studying women’s brains because, “The menstrual cycle would mess up the data.”
While that’s true, it’s exactly what Brizendine studies, and needs to study to women and emotional disorders. She points out that there’s a two to one ratio of depression in adult women versus men. That rises from a 1:1 ratio in childhood. So what happens in human development to make the brains change?
One of the images Brizendine shows in her talk.
Brizendine points out that all brains start out as female. Eight weeks into fetal development, a boy’s testes bathe the brain in testosterone and changes the brain so that the “area for sexual pursuit” becomes 2-2.5 times as large as in the female brain, which ends up “unperturbed by testosterone”. For about two years, baby brains pump out a good deal of testosterone or estrogen, but then level off, creating a “childhood pause”, when children aren’t heavily affected by hormones. Still, they play very differently – girls engage in relationship play, while boys engage in superhero play.
In teens, girls are suddenly “biffeted by double tsunamis” of estrogen and progesterone. These waves cause changes in the brain, literal growth and retraction of synapes in some regions. Teen boys at the same time suddenly have a 25 times increase in testosterone. “You have to remember, suddenly they’re running on jet fuel.”
The “mommy brain” is heavily affected by oxytocin, “the pair-bonding molecule.” Females experience this from menses through their fertile life, while men mostly get it after orgasm. “Have more sex, it’s good for you,” she tells us. The female brain, shaped in part by this chemical, is better at emotional detail, nuance and detecting non-verbal cues. Testosterone can actually screw this up – a study shows that injecting women with testosterone makes neutral faces look angry. On the other hand, giving men inhalable oxytocin makes men more trusting of financial advisors.
Why does this matter? Psychological disorders are related to gender. Females are twice as likely to be depressed as men. Autism is 8 times more common in men, and violent agression is twenty times more likely in men. We need to understand how brains are different from gender to understand these diseases.
She closes by pointing out that, in the 1800s, women had on average 14 pregnancies and 10 births. The lifespan was 39, and most women never experienced menopause. Now women have part of their lives that occurs after childbearing and rearing – “there’s a new phase of life beyond mothering” that she’s personally experiencing and wants to study.
The fundamental point – there’s no such thing as a unisex brain, and we need to understand it to understand how humans actually work.
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