The most obvious example is what happens to many patients who take selective serotonin-reuptake inhibitors (SSRIs), a class of antidepressants: Their libidos shut down. SSRIs increase brain levels of the neurotransmitter serotonin, which helps regulate mood, but the drugs have also become notorious for dampening sex drive.
New theory: Sex drive is a reflex
These drug reactions serve to show us that our sex drive is at least partly a function of our body chemistry. But emotions have a major role as well. We know that, instinctivelybut now scientists are starting to try to explain it.
One theory is that sex is a reflexautomatic except that your emotions can override it.
The classic reflex test is the one where the doctor hits the tendon in your knee with a mallet, and the tendon contracts, all by itself. "Let's say the doctor is trying to do this test, and outside there's a robbery with gunshots," posits Irwin Goldstein, MD, director of San Diego Sexual Medicine and the editor in chief of The Journal of Sexual Medicine. Your brain will override the reflex; your leg will stay still.
Now, Dr. Goldstein says, consider the sex reflex. "You're rubbing up against another person on a dance floor," he suggests. You'll feel desire, all right. But only "if ..." says Dr. Goldstein. "If you're not worried about safety, if it has been a nice day, if, if, if ..."
And if not? Your brain can inhibit the response and you just won't be "interested."