What Sex Does to a Man's Brain

You're sitting behind the wheel of your van at an everlasting traffic light. The only thing slower than the traffic is your perception of time's passage.

Then you notice her.

She appears at the curb, waiting to cross. No, she's not the love of your life. She's more like the heat of the moment. It's fortunate that your wife isn't there, otherwise you'd be in deep trouble as you take in the stranger's hips and breasts, and the way her waist scoops in to accentuate both. Time is enhanced; there's a pleasing buzz connecting your temples.

Your reaction is automatic, reflexive, and quite possibly the most powerful one you'll have this day. It temporarily blots out your long-range commitments — that 10-year marriage, that kid in second grade, that responsibility to keep eyes forward at traffic lights. You've surrendered control; you're captivated by the pleasure in the vision.

"You dog!" you may whisper under your breath, embarrassed by what you're envisioning as you sit there in your family van. But it might be more correct to say, "You dopamine fiend!" As a neuroscientist of 25 years, I know that your brain is command central for everything sexual.

When you spot the object of your desire, the neurotransmitter dopamine lights up areas deep within the brain, triggering feelings of pleasure, motivation, and reward. (Cocaine acts the same way.) You feel a rush, and your heartbeat quickens. Attraction, too, is a powerful drug. The brain stem also gets into the act, releasing phenylethylamine (PEA), which speeds up the flow of information between nerve cells. It's no wonder your neck and eyeballs track her every movement.

But she's not gawking back at you, and it's not just because you're driving a family bus with a paint scrape on the fender. Her brain acts very differently from yours. You're keyed in to beauty, shape, fantasy, and obsession; on some biological level that she may be unaware of, she's trolling for a mate who will sire healthy children and protect and provide for her and them. And yes, maybe even buy them a family van.

Learn the 50 things women wish men knew .

Her goals are programmed for the long range; yours are often shockingly short term, right up to and including thoughts of pedestrianophilia. And she knows it, which is why she presses those short-term buttons shotgun-style: She never knows when a suitable mate might be looking.

The whole encounter can leave you quivering with pleasure, hoping for more.

It can also hijack and ruin your life.

And between the "walk" and "don't walk" signals of delight and disaster, your brain is sorting information, making choices, spurring actions. But you don't want to passively accept all that, especially because your whole life is riding on the choices you make.

That's where I come in. I know the brain processes behind the temptations, and I can help you steer clear of trouble. After all, that woman in the crosswalk could help you realize your destiny, or derail it entirely. All the more reason to get to know that big sex organ between your ears so you can control the smaller, less important one between your legs.

Why You've Always Been Horny

You've been lit up on testosterone right from the start, even when you were just a multicelled notion in your mother's womb. The inherited Y chromosome that makes you male (thanks, Dad) triggers two bursts of testosterone that change your brain and body.

The first produces a male brain: one that's more interested in objects, actions, and competition. The left (parietal) lobe flourishes in the testosterone bath and helps you visualize objects in three dimensions (good for catching a football or watching a woman cross the street), and it boosts your aptitude in mathematics (that's how you estimate that she's about a 34DD). In addition, testosterone beefs up your hypothalamus, the area of the brain that's interested in sex. The hypothalamus is twice as large in men as it is in women.

Why You Become Hornier as a Teen
That's when the second big burst of testosterone hits, causing your hair to sprout everywhere, your voice to flip from Norah Jones to James Earl Jones, and your interest in third base to go from literal to metaphorical. (Touch 'em all!) Your body now harbors 20 times the level of testosterone found in girls your age, which accounts for your sexual obsessions.
Unfortunately, your brain is maladapted for sociability, so she can overwhelm you with words, and all you have to counter them is silent (thank goodness) adolescent lust. It's an advantage she has that you'll never make up. On your side of the ledger: Your left brain — the planning center — is massive, which helps in planning the Panama Canal, a rocket launch, or a lifetime of wedded bliss.