Nine men and nine women file into a room for a scientific study. A tubing system set up with a small pump continuously draws blood from all of the volunteers to test the chemicals that course through their veins. Simultaneous cardiovascular tests measure their blood pressures and heart rates through small finger cuffs.
Then, the researchers turn on the porn.
Doctors have long had interest in how sexual arousal and orgasm are caused by biological effects in the body and have made a great deal of progress. The field of psychoneuroendocrinology, as the somewhat unwieldy name suggests, seeks to know how psychology, neurology and hormones interact in the human body.
Researchers have actually done the study I mentioned above. After showing the pornography, they wait for the subjects to orgasm and figure out which chemicals are in their bloodstreams. Two of the most important chemicals are dopamine and prolactin, but each play very different roles.
Dopamine is simply the chemical that makes us want. Say you go to a restaurant and order your favorite meal. As you wait, your desire for the food grows. At last, when you bite into the steak or hamburger or delicious chocolate dessert, there is a moment of bliss.
The feeling of bliss? Dopamine turning on pathways in the brain.
Dopamine is a very potent neurotransmitter. Not only is dopamine important to biologically essential activities like eating and evolutionarily essential activities like sex, but it has also been implicated in drug addiction, gambling compulsion and love passion. Researchers still debate whether love passion can be a diagnosable mental disorder, called love addiction. Though the consensus is that love doesn’t quite fill the criteria of addiction, it still activates the same brain regions and neurotransmitters as substance addiction.
Dopamine is present in the bloodstreams of the subjects of the sexual arousal study as they are turned on by the porn (“erotic film” in the words of researchers from University of New England who conducted the study). However, the hormone prolactin only appears if the subjects orgasm and is known as the “sexual satiation hormone” (it also causes lactation during pregnancy, but that’s a story for another time).
Dopamine and prolactin have a good cop, bad cop relationship in the body during and after sex. People in the throes of sexual arousal experience a flood of dopamine in the brain. Dopamine and prolactin both peak just before and during the moment of orgasm. Prolactin is the hormone that sees dopamine going out of control and tells it, “Take it easy.”
Both hormones have to have the correct balance in order for sex to work as it should. Too much dopamine relative to prolactin could cause a sensory overload; too much prolactin relative to dopamine has been shown to cause impotence in men and a decrease in libido.
These are just a couple of the neurological effects of sexual arousal and orgasm, but there are other physical effects as well. Vaginal lubrication in women and pre-ejaculate in men are both associated with sexual arousal, and for good reason – without lubrication, sex would be extremely painful.
Lubrication is a mixture of many chemicals including water, acetic acid (which gives vinegar its distinctively sour taste) and urea (the main component of urine). Vaginal lubrication is rather acidic with a pH between 3.5 and 4, so semen must counteract this acidity by being basic with a pH closer to 8 (a neutral pH is 7). As sexual arousal causes engorged blood vessels in the genitalia, fluid seeps in through the vaginal walls to lubricate.
Vaginal dryness is called dyspareunia and is considered a type of sexual pain disorder (if you wonder why, consider how much friction is involved in sexual intercourse). Causes range from lack of sexual arousal to hormonal changes involved in menopause and aging, and even to medications like antihistamines and birth control pills.
There unfortunately isn’t enough room in this whole newspaper to talk about all of the science of sex. If you’re interested, a good place to go would be the book Bonk by Mary Roach. In the meantime, don’t think of this as too much information about the fun of sexual activity; think of it as a new way to look at sex, or at the very least, a conversational icebreaker.
AMY STEWART can be reached at firstname.lastname@example.org.