The Male Brain Read online

  ALSO BY LOUANN BRIZENDINE, M.D.

  The Female Brain

  To the men in my life:

  My husband, Dr. Samuel Herbert Barondes

  My son, John “Whitney” Brizendine

  My brother, William “Buzz” Brizendine II

  And in memory of my father, Reverend William Leslie Brizendine

  CONTENTS

  Acknowledgments

  The Male Brain (diagram)

  The Cast of Neurohormone Characters

  Phases of a Male’s Life

  INTRODUCTION

  What Makes a Man

  ONE

  The Boy Brain

  TWO

  The Teen Boy Brain

  THREE

  The Mating Brain: Love and Lust

  FOUR

  The Brain Below the Belt

  FIVE

  The Daddy Brain

  SIX

  Manhood: The Emotional Lives of Men

  SEVEN

  The Mature Male Brain

  EPILOGUE

  The Future of the Male Brain

  APPENDIX

  The Male Brain and Sexual Orientation

  Notes

  References

  ACKNOWLEDGMENTS

  This book had its beginnings during my educational years at U.C. Berkeley, Yale, Harvard, and U.C. London, so I would like to thank those teachers who most influenced my thinking during those years: Frank Beach, Mina Bissell, Harold Bloom, Marion Diamond, Walter Freeman, Florence Haseltine, Richard Lowenstein, Daniel Mazia, Fred Naftolin, Stanley Jackson, Roy Porter, Carl Salzman, Leon Shapiro, Rick Shelton, Gunter Stent, Frank Thomas, George Valliant, Clyde Willson, Fred Wilt, Richard Wollheim.

  During my years on the faculty at Harvard and UCSF, my thinking has been influenced by: Cori Bargman, Samuel Barondes, Sue Carter, Regina Casper, Lee Cohen, Mary Dallman, Allison Doupe, Deborah Grady, Mel Grumbach, Leston Havens, Joel Kramer, Fernand Labrie, Sindy Mellon, Michael Merzenich, Joseph Morales, Kim Norman, Barbara Parry, Victor Reus, Eugene Roberts, Nirao Shah, Carla Shatz, Stephen Stahl, Marc Tessier-Lavigne, Rebecca Turner, Owen Wolkowitz, Chuck Yingling, and Ken Zack.

  My colleagues, staff, residents, medical students, and patients in the Women’s and Hormone Clinic. I would especially like to thank my faculty members at the clinic: Lyn Gracie Adams, Steve Hamilton, Dannah Hirsch, Jane Hong, Shana Levy, Faina Novosolov, and Elizabeth Springer.

  And for their friendship and support throughout: Lynne Benioff, Marc Benioff, Diane Cirincione, Janet Durant, Adrienne Larkin, Sharon Melodia, Nancy Milliken, Jeanne Roberston, Sandy Robertson, Alla Spivak, and Jodi Yeary.

  The work presented in this book has been based on and greatly benefited from the research and writings of: Marty Altemus, Arthur Arnold, Arthur Aron, Simon Baron-Cohen, Andreas Bartels, Frank Beach, Jill Becker, Sherri Berenbaum, Karen Berkley, Jeff Blaustein, Marc Breedlove, Lucy Brown, David Buss, Larry Cahill, Anne Campbell, Sue Carter, David Crews, Susan Davis, Karl Deisseroth, Geert De Vries, Catherine Dulac, Elisa Epel, Helen Fisher, David Geary, Jay Giedd, Jill Goldstein, Louis Gooren, Mel Grumbach, Andy Guay, Elizabeth Hampson, Bob Handa, James Herman, Melissa Hines, Gert Holstege, Sarah Hrdy, Janet Hyde, Tom Insel, Bob Jaffe, Doreen Kimura, Eleanor Maccoby, Dev Manoli, Helen Mayberg, Martha McClintock, Erin McClure, Bruce McEwen, Michael Meaney, Toni Pak, Barbara Parry, Don Pfaff, David Rubinow, Robert Sapolsky, Peter Schmidt, Nirao Shah, Barbara Sherwin, Elizabeth Spelke, Dick Swaab, Jane Taylor, Shelley Taylor, Rebecca Turner, Kristin Uvnas-Moberg, Victor Viau, Myrna Weissman, Sandra Witelson, Sam Yen, Kimberly Yonkers, Elizabeth Young, Larry Young, and the many other scientists whose work I have cited in this book.

  I would also like to thank the foundations and supporters of my work: the Lynne and Marc Benioff Family, the Lawrence Ellison Medical Foundation, National Center for Excellence in Women’s Health at UCSF, the Osher Foundation, the Staglin Family Music Festival for Mental Health, the Salesforce.com Foundation, the Stanley Foundation, and the UCSF Department of Psychiatry.

  This book was written and rewritten with the assistance of Toni Robino. I owe her the greatest debt of gratitude.

  I would especially like to thank Diane Middlebrook and the Literary Salon. Diane set the stage for me to begin writing; she read many drafts of my work and was, and is, an inspiration even past her untimely death.

  Amy Hertz believed in this book from day one and deserves special thanks for helping shape my thinking and writing over the years.

  I am very thankful to those who worked to make this book happen: Julie Sills, Stephanie Bowen, Elizabeth Rendfleisch, Mark Birkey, Gary Stimeling, Lorraine Glennon, Diane Salvatore, my ever encouraging agent, Lisa Queen of Queen Literary, and my dedicated publicity manager at Random House, Rachel Rokicki.

  I am grateful to my editor at Random House, Kris Puo-polo, who supported me with intelligence, skill, and dedication through many years of writing, rewriting, starts, and stops.

  I also want to thank my son, John “Whitney,” for graciously allowing me to use many of his personal stories and whose help in understanding the world of boys, teens, and young men has been invaluable. His sense of humor and determination continue to inspire me.

  Most of all I thank my husband and soul mate, Sam Barondes, for everything—his insights into the world of men, his wisdom, levity, intelligence, critiques, editorial advice, scientific acumen, tolerance, empathy, and love.

  The Male Brain

  Scientists think of brain areas like the ACC, TPJ, and RCZ as being “hubs” of brain activation, sending electrical signals to other areas of the brain, causing behaviors to occur or not occur.

  1. MEDIAL PREOPTIC AREA (MPOA): This is the area for sexual pursuit, found in the hypothalamus, and it is 2.5 times larger in the male. Men need it to start an erection.

  2. TEMPORAL PARIETAL JUNCTION (TPJ): The solution seeker, this “cognitive empathy” brain hub rallies the brain’s resources to solve distressing problems while taking into account the perspective of the other person or people involved. During interpersonal emotional exchanges, it’s more active in the male brain, comes on-line more quickly, and races toward a “fix-it-fast” solution.

  3. DORSAL PREMAMMILLARY NUCLEUS (DPN): The defend-your-turf area, it lies deep inside the hypothalamus and contains the circuitry for a male’s instinctive one-upmanship, territorial defense, fear, and aggression. It’s larger in males than in females and contains special circuits to detect territorial challenges by other males, making men more sensitive to potential turf threats.

  4. AMYGDALA: The alarm system for threats, fear, and danger. Drives emotional impulses. It gets fired up to fight by testosterone, vasopressin, and cortisol and is calmed by oxytocin. This area is larger in men than in women.

  5. ROSTRAL CINGULATE ZONE (RCZ): The brain’s barometer for registering social approval or disapproval. This “I am accepted or not” area keeps humans from making the most fundamental social mistake: being too different from others. The RCZ is the brain center for processing social errors. It alerts us when we’re not hitting the mark in our relationship or job. During puberty, it may help males reset their facial responses to hide their emotions.

  6. VENTRAL TEGMENTAL AREA (VTA): It’s the motivation center—an area deep in the center of the brain that manufactures dopamine, a neurotransmitter required for initiating movement, motivation, and reward. It is more active in the male brain.

  7. PERIAQUEDUCTAL GRAY (PAG): The PAG is part of the brain’s pain circuit, helping to control involuntary pleasure and pain. During sexual intercourse, it is the center for pain suppression, intense pleasure, and moaning. It is more active during sex in the male brain.

  8. MIRROR-NEURON SYSTEM (MNS): The “I feel what you feel” emotional empathy system. Ge
ts in sync with others’ emotions by reading facial expressions and interpreting tone of voice and other nonverbal emotional cues. It is larger and more active in the female brain.

  9. ANTERIOR CINGULATE CORTEX (ACC): It’s the worry-wart, fear-of-punishment area and center of sexual performance anxiety. It’s smaller in men than in women. It weighs options, detects conflicts, motivates decisions. Testosterone decreases worries about punishment. The ACC is also the area for self-consciousness.

  10. PREFRONTAL CORTEX (PFC): The CEO of the brain, the PFC focuses on the matter at hand and makes good judgments. This “pay total attention to this now” area also works as an inhibiting system to put the brakes on impulses. It’s larger in women and matures faster in females than in males by one to two years.

  THE CAST OF NEUROHORMONE CHARACTERS

  (how hormones affect a man’s brain)

  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.

  MÜLLERIAN 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.

  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 and builds trust circuits, romantic-love circuits, and attachment circuits in the brain. He reduces stress 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.”

  PROLACTIN—Mr. Mom. He causes sympathetic pregnancy (couvade syndrome) in fathers-to-be and increases dads’ ability to hear their babies cry. He stimulates connections in the male brain for paternal behavior and decreases sex drive.

  CORTISOL—The Gladiator. When threatened, he is angry, fired up, and willing to fight for life and limb.

  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.

  PHASES OF A MALE’S LIFE

  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.

  INTRODUCTION

  What Makes a Man

  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 neuroscientific research and theory. Powerful new scientific tools, such as genetic and 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, making decisions, noticing facial exp
ression, 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 (Müllerian 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.