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 spectacular 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 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 processing brain 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 some of 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.