What happens when you drop a male rat into a cage with a receptive female rat? First you see a frenzy of copulation. Gradually, the male's enthusiasm wanes and, finally, he goes off to take a well-earned nap. He is sexually satiated. It will take 15 days for him to recover his full libido--that is, for his brain chemistry to return to homeostasis (equilibrium). There is one way to override any sluggishness, however: supply a novel female. Consider this story:
A guinea pig called Sooty enjoyed a night of passion with twenty-four females after fooling his way into their cage in south Wales. Sooty wooed the lady guinea pigs, one by one, and has now become the proud father of forty-two baby guinea pigs. . . . "He was absolutely shattered. We put him back in his cage and he slept for two days." Romeo Guinea Pig Causes Baby Boom Our genes really don't want unfertilized females left unserviced.
Think some vestige of this program is still encoded in human brains? What about polyamorous hunter-gatherer men and women, sultans with harems, porn users in search of the next novel image, and today's revolving door marriages?
Whether you act on your impulses or not, your genetic programming is acting on you. Where is this program pushing us these days? Not only where our genes want us to go--exploitation of the occasional chance to fertilize multiple mates--but often beyond, into empty compulsion. And all because times have changed. As Burnham and Phelan explain in Mean Genes: From Sex to Money to Food, Taming Our Primal Instincts, our environment has changed, leaving our reward circuitry very vulnerable. We are molded to meet conditions that prevailed during our brain's millions of years of development. And to the extent that present day conditions are different from ancestral conditions, the ancestral genetic advice encoded in our DNA is wrong. (Richard Dawkins, A Devil's Chaplain, p. 103)
Cave girls were no doubt cute, but their erotically posed images weren't airbrushed to perfection and projected over every visible surface. There was less opportunity for hooking up with exciting new mates you barely knew. No singles bars, no tantra weekends, and no schools with hundreds of cute, sexily clad strangers of the opposite sex. Here's the danger in our modern circumstances: When a mammal's brain hasn't adapted to the intensity and quantity of a stimulus, that stimulus registers as a superstimulus, and dopamine rises sharply in the reward circuitry.
The preceding examples can be superstimuli for our hunter-gatherer brains. Internet porn is an extreme superstimulus. It's on tap twenty-four/seven, free of social constraints, and every click supplies a "novel mate" beckoning to be serviced. Chasing after today's potent array of superstimulation can easily overload our vulnerable reward circuitry. Without realizing why, we may begin to experience withdrawal symptoms, cravings for even more frequent stimulation, and, sometimes, enduring brain changes.
The more extreme the stimulation (whatever our individual thresholds), the more dopamine surges in our reward circuitry. And the lower it drops afterward (or the less sensitive we are to it, due to down regulation of nerve cell receptors). Dopamine balance matters. For example, high dopamine is associated with compulsions, anxiety, risky behavior, and so forth, while low dopamine is associated with conditions like social anxiety, depression, inability to feel pleasure, and lack of ambition.
Most of us learn about the high-leads-to-hangover cycle fairly early by drinking too much alcohol. So why are we so likely to reach for short-lived, intense stimulation even when it begins to set off neurochemical hangovers? Usually because we aren't getting enough of the other rewards our brain finds gratifying.
Many of us have lost a lot of the comfort of close companionship that our ancestors enjoyed. We don't live in tribes, and our extended family may be far away. We spend way more hours staring at monitors than engaging in friendly human interaction. Our brain's primitive limbic system is starved for the healthy rewards that come from companionship and touch, which makes us more susceptible to overindulging, addictions, and compulsions.
Let's say we choose to comfort ourselves with a big dose of today's super-sexy stimulation. After dopamine soars in response to extreme stimulation, it drops unnaturally low. Withdrawal symptoms, such as restlessness, irritability, frustration, desire for isolation, and apathy are signals that we're not yet back to equilibrium at a brain chemical level.
So why the massive horniness? During recovery, we may feel uneasy or depressed, as if some key ingredient for our happiness is missing. As a consequence, we're very susceptible to cues our brain associates with rapid relief from discomfort. When we spot one, our reward circuitry starts yapping and bouncing around like a crazed Jack Russell terrier. Surging dopamine is hard to ignore, so we want to "feed it," just to shut it up.
Yet if we climax now, we can easily fall into an accelerating cycle, medicating ourselves with more stimulation every time we get The Urge. Strapped onto this roller coaster of peaks and drops, we may forget entirely what balance feels like. Unfortunately, we have to go all the way through the misery of withdrawal to experience balance again. There are no shortcuts, and if we're seriously hooked, we may need longer, due to more lasting changes in the brain.
For example, a protein known as Delta FosB remains in addicts' brains for a month or two, making relapse more likely. Mae West"Too much of a good thing . . . is even better!" said the witty Ms. Mae West. However, too much intense stimulation of the reward circuitry is not better. It's worse. The risk is ending up on a high-speed treadmill, trying to stay ahead of withdrawal symptoms. As our sensitivity to dopamine decreases, we may need more and more stimulation to feel good, even briefly.
UPDATE (2014): Researchers have shown that ejaculation, even twice a week, shrinks the dopamine-producing neurons in the VTA, which reduces a male's response to the pleasure of morphine. This also happens with repeated heroin use in both rats and humans. Scientists have also learned that amphetamine activates the exact same nerve cells as orgasm, urging the brain to "remember and repeat." In other words, drugs of abuse "work" because they're hijacking the mechanisms that evolved to make us want sex...and yet experience aftereffects from too frequent sex.
In contrast with our ancestors' frugal lifestyles, our lifestyle doesn't protect us from overindulgence. Too much stimulation, followed by frequent lows, means we are sometimes riddled with unusually intense cravings for relief. When we're out of balance, we're voracious consumers, but less satisfied humans. Our recurring, urgent sense of lack heavily influences the choices we make-without our conscious awareness.
Once we recognize the vulnerability of our reward circuitry in the face of today's superabundance, we can see the real challenge before us. It is to get our dopamine levels back in balance and keep them there. Then we can enjoy the occasional indulgence without falling into an uncomfortable cycle of highs and lows. Balanced dopamine is associated with feelings of well-being and satisfaction, pleasure in accomplishing tasks, healthy libido, good feelings toward others, motivation, optimism, sound choices, healthy risk-taking, realistic expectations and healthy bonds with others.
For science buffs: Growing evidence of a lingering post-orgasm cycle (links to studies)