The Male Brain (2 page)

TESTOSTERONE
--Zeus. King of the male hormones, he is dominant, aggressive, and all-powerful. Focused and goal-oriented, he feverishly builds all that is male, including the compulsion to outrank other males in the pecking order. He drives the masculine sweat glands to produce the come-hither smell of manhood--androstenedione. He activates the sex and aggression circuits, and he's single-minded in his dogged pursuit of his desired mate. Prized for his confidence and bravery, he can be a convincing seducer, but when he's irritable, he can be the grouchiest of bears.

VASOPRESSIN--
The White Knight. Vasopressin is the hormone of gallantry and monogamy, aggressively protecting and defending turf, mate, and children. Along with testosterone, he runs the male brain circuits and enhances masculinity.

MULLERIAN INHIBITING SUBSTANCE (MIS)
--Hercules. He's strong, tough, and fearless. Also known as the Defeminizer, he ruthlessly strips away all that is feminine from the male. MIS builds brain circuits for exploratory behavior, suppresses brain circuits for female-type behaviors, destroys the female reproductive organs, and helps build the male reproductive organs and brain circuits.

and builds trust circuits, attachment circuits in the hormones, lowers men's blood pressure, and plays a major role in fathers' bonding with their infants. He promotes feelings of safety and security and is to blame for a man's "postcoital narcolepsy."
OXYTOCIN
--The Lion Tamer. With just a few cuddles and strokes, this "down, boy" hormone settles and calms even the fiercest of beasts. He increases empathic ability

increases Mom. He syndrome)

dads' ability to hear causes sympathetic in fathers-to-be and their babies cry. He

ANDROSTENEDIONE
--Romeo. The charming seducer of women. When released by the skin as a pheromone he does more for a man's sex appeal than any aftershave or cologne.

DOPAMINE
--The Energizer. The intoxicating life of the party, he's all about feeling good, having fun, and going for the gusto. Excited and highly motivated, he's pumped up to win and driven to hit the jackpot again and again. But watch out--he is addictively rewarding, particularly in the rough-and-tumble play of boyhood and the sexual play of manhood, where dopamine increases ecstasy during orgasm.

ESTROGEN
--The Queen. Although she doesn't have the same power over a man as Zeus, she may be the true force behind the throne, running most of the male brain circuits. She has the ability to increase his desire to cuddle and relate by stimulating his oxytocin.

Hormones can determine what the brain is interested in doing. Their purpose is to help guide social, sexual, mating, parenting, protective, and aggressive behaviors. They can affect being rough-and-tumble, competing in sports or attending sporting events, solving problems, interpreting facial expressions and others' emotions, male-male bonding, dating and mating, ogling attractive females, forming sexual and pair-bond relationships, protecting family and turf, fantasizing, masturbating, and pursuing sex.

YOU COULD say that my whole career prepared me to write my first book,
The Female Brain
. As a medical student I had been shocked to discover that major scientific research frequently excluded women because it was believed that their menstrual cycles would ruin the data. That meant that large areas of science and medicine used the male as the "default" model for understanding human biology and behavior, and only in the past few years has that really begun to change. My early discovery of this basic inequity led me to base my career at Harvard and the University of California-San Francisco (UCSF) around understanding how hormones affect the female and male brains differently and to found the Women's Mood and Hormone Clinic. Ultimately that work led me to write
The Female Brain
, which addressed the brain structures and hormonal biology that create a uniquely female reality at every stage of life.

The distinct brain structures and hormonal biology in the male similarly produce a uniquely male reality. But as I considered writing
The Male Brain
, nearly everyone I consulted made the same joke: "That will be a short book! Maybe more of a pamphlet." I realized that the idea that the male is the default-model human still deeply pervades our culture. The male is considered simple; the female, complex.

Yet my clinical work and the research in many fields, from neuroscience to evolutionary biology, show a different picture. Simplifying the entire male brain to
just
the "brain below the belt" is a good setup for jokes, but it hardly represents the totality of a man's brain. There are also the seek-and-pursue baby boy brain, the must-move-or-I-will-die toddler brain; the sleep-deprived, deeply bored, risk-taking teen brain; the passionately bonded mating brain; the besotted daddy brain; the obsessed-with-hierarchy aggressive brain;
and the fix-it-fast emotional brain
. In reality, the male brain is a lean, mean problem-solving machine.

The vast new body of brain science together with the work I've done with my male patients has convinced me that through every phase of life, the unique brain structures and hormones of boys and men create a male reality that is fundamentally different from the female one and all too frequently oversimplified and misunderstood.

Male and female brains
are different from the moment of conception. It seems obvious to say that all the cells in a man's brain and body are
male
. Yet this means that there are deep differences, at the level of every cell, between the male and female brain. A male cell has a Y chromosome and the female does not. That small but significant difference begins to play out early in the brain as genes set the stage
for later amplification by hormones
. By eight weeks after conception, the tiny male testicles begin to produce enough testosterone to marinate the brain and fundamentally alter its structure.

Over the course of a man's life, the brain will be formed and re-formed according to a blueprint drafted both by genes and male sex hormones. And this male brain biology produces his distinctly male behaviors.

The Male Brain
draws on my twenty-five years of clinical experience as a neuropsychiatrist. It presents research findings from the advances over the past decade in our understanding of developmental neuroendocrinology, genetics, and molecular neuroscience. It offers samplings from neuropsychology, cognitive neuroscience, child development, brain imaging, and psychoneuroendocrinology. It explores primatology, animal studies, and observation of infants, children, and teens, seeking insights into how particular behaviors are programmed into the male brain by a combination of nature and nurture.

During this time, advances in genetics, electrophysiology, and noninvasive brain-mapping technology have ignited a revolution in Powerful new chemical tracers, positron-emission tomography (PET) and functional magnetic resonance imaging (fMRI), now allow us to see inside the working human brain while it's solving problems, producing words, retrieving memories, neuroscientific research and theory. scientific tools, such as genetic and making decisions, noticing facial expression, falling in love, listening to babies cry, and feeling anger, sadness, or fear. As a result, scientists have recorded a catalog of genetic, structural, chemical, hormonal, and brain-processing
differences between women and men
.

In the female brain, the hormones estrogen, progesterone, and oxytocin predispose brain circuits toward female-typical behaviors. In the male brain, it's testosterone, vasopressin, and a hormone called MIS (Mullerian inhibiting substance) that have the earliest and most enduring effects. The behavioral influences of male and female hormones on the brain are major. We have learned that men use different brain circuits to process spatial information and solve emotional problems. Their brain circuits and nervous system are wired to their muscles differently--especially in the face. The female and male brains hear, see, intuit, and gauge what others are feeling in their own special ways. Overall, the brain circuits in male and female brains are very similar, but men and women can arrive at and accomplish the same goals and tasks using different circuits.

We also know that men have two and a half times the brain space devoted to sexual drive in their hypothalamus. Sexual thoughts flicker in the background of a man's visual cortex all day and night, making him always at the ready for seizing sexual opportunity. Women don't always realize that the penis has a mind of its own--for neurological reasons. And mating is as important to men as it is to women. Once a man's love and lust circuits are in sync, he falls just as head over heels in love as a woman--perhaps even more so. When a baby is on the way, the male brain changes in specific and dramatic ways to form the daddy brain.

Men also have larger brain centers for muscular action and aggression. His brain circuits for mate protection and territorial defense are hormonally primed for action starting at puberty. Pecking order and hierarchy matter more deeply to men than most women realize. Men also have larger processors in the core of the most primitive area of the brain, which registers fear and triggers protective aggression--the amygdala. This is why some men will fight to the death defending their loved ones. What's more, when faced with a loved one's emotional distress, his brain area for problem solving and fixing the situation will immediately spark.

I must have been dimly aware of this long catalog of distinctive male behaviors when I first found out, twenty-one years ago, that the baby I was carrying had a Y chromosome. I immediately thought,
Oh dear. What am I going to do with a boy?
Up until that moment, I realized, I had unconsciously been thinking
It's a girl!
and feeling confident that my own female life experiences could guide me in raising a daughter. I was right to be nervous. My lack of boy-smarts was about to matter more than I imagined. I now know from my twenty-five years of research and clinical work that both men and women have a deep misunderstanding of the biological and social instincts that drive the other sex. As women, we may love men, live with men, and bear sons, but we have yet to understand men and boys. They are more than their gender and sexuality, and yet it is intrinsic to who they are. And it further complicates matters that neither women nor men have a good sense of what the others' brains or bodies are doing from one moment to the next. We are mostly oblivious to