Being a woman, says neuropsychiatrist Louann Brizendine, is like having giant, invisible antennae that reach out into the world, constantly aware of the emotions and needs of those around you.
Though the antennae are metaphorical, the brain circuitry and hormones that make women so much more attuned — and some would say beholden to — the emotions of others are very real.

They're the subject of Brizendine's book, The Female Brain. In it, the founder of the University of California-San Francisco Women's and Teen Girls' Mood and Hormone Clinic describes the physical and hormonal differences in the female brain, from fetus to grandmother. Using studies on hormones, development and psychology by scientists in multiple fields as well as her own clinical experience, Brizendine sets out to show the ways in which the female brain is different from the male brain.

This has always been fraught territory in the arena of gender politics. Since the 19th century, social wars have raged over whether the sexes are more alike or different, and, if those differences exist, whether they're innate or a result of societal expectations.

The female brain is a machine built for connection, Brizendine says. It's a result of eons of evolution that allowed women to tell what their pre-verbal infants needed and predict what bigger, more aggressive males were going to do.

As a scientist and physician who came of age in the 1970s when the mere notion that brains were anything but unisex was anathema, she's convinced of the truth of her ideas but still worried that acknowledging differences will lead to women being discriminated against in the workplace. Yet acknowledging that women are to some extent hard-wired to nurture is a positive, not a negative, both for the next generation and for the general well-being of society, she says.

"There's still the feeling among women who are just hovering below the glass ceiling that the science described in this book is going to highlight differences which will hurt their chances of breaking through," Brizendine says.

For example, just last year Harvard's now-former president Larry Summers created an enormous controversy when he said that one reason women may not rise as high in the sciences is that they're not as innately gifted in those areas.

Janet Hyde, a professor of psychology and women's studies at the University of Wisconsin-Madison, has written extensively on what she calls "the gender similarities hypothesis." Numerous studies have found that except in a very few areas — physical strength, physical aggression, incidences of masturbation and attitudes about casual sex — on the whole men and women are much more alike than they are different.

"If you make the argument that 'Gosh, our brains are totally different and we're totally different and yet we want equal access to medical school and we want equal pay for equal work,' " women will pay a price in advancement, Hyde says.

But others clearly see differences. Whether those differences are based on genetics, hormones or some interplay of the two isn't yet known, says Sandra Witelson, a cognitive neuroscientist at the Michael G. DeGroote School of Medicine at McMaster University in Canada.

"There are clear differences in the brain between men and women, both in the structure and anatomy and the chemistry, which includes hormones and neurotransmitters and what's connected to what," she says.

She cites girls who have a hormone disorder that causes them to have higher testosterone levels in utero. "In these girls, their play patterns, their spatial ability and even their sexual orientation are much closer to the male pattern."

But while sex-based differences are clearly present, David Rubinow, chairman of the department of psychiatry at the University of North Carolina at Chapel Hill, says those differences don't exclude the effect of non-sex-related factors involving biology, culture or the environment.

It's discussing the "Mommy brain" that's most controversial in some quarters. Brizendine catalogs the hormonal cascades triggered by being pregnant, nursing and simply being constantly physical with children. Fathers who spend lots of time with their children and adoptive mothers also get the one-two neurological-hormonal punch, but it's strongest in those who give birth and nurse, Brizendine says.

And in a country where women are educated at higher rates than men, society has not done a good job of figuring out how to integrate the child-rearing portion of their lives into the world of work, she says.

"We need to find a place in our society for working mothers with young children that acknowledges their life stage." And it is only a stage — five to eight years — not their entire lives, Brizendine says.

The last thing Brizendine wants to say is that biology is destiny.

"Having a deeper understanding of what those hormones are doing to the opposite sex should give us a better understanding of male and female behavior and let men and women both be allowed to maximize all kind of choices."