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Why Sex Feels Good: The Science Behind Orgasms

New brain studies explain how pleasure really works.

The following is an excerpt from  “The Aesthetic Brain” by Anjan Chatterjee with permission from Oxford University Press USA, © 2013 by Oxford University Press.  Click here to buy the book. 

Before I realized what was happening, the patient reached down between my legs and grabbed my genitals. It was 1985, in the middle of the night during my medicine internship. I was working about 110 hours a week. Every third night I was on call and felt lucky if I got a couple of hours of sleep. That night, I was taking care of this patient for another intern. On my endless “to do” list was the task of placing an intravenous line. When I got to her room it was dark. I didn’t know what her medical condition was. I was focused on starting her IV and then moving on to my next task. I turned on the soft light over her hospital bed and gently woke her. She seemed calm. I loosened her restrained arm to look for a good vein. That was when she grabbed me.

Even in my sleep-, food-, and sex-deprived state, I recognized that my charms were not the reason for her attention. She acted indiscriminately.  She grabbed nurse’s breasts and students’ buttocks  with the same enthusiasm. I had not yet started my neurology residency and did not know that she was suffering from a human version of Klüver-Bucy syndrome. The syndrome is named after Heinrich  Klüver, a psychologist, and Paul Bucy, a neurosurgeon,  who observed that rhesus monkeys changed profoundly  when their anterior-medial temporal lobes were removed. They became placid. They were no longer fearful of objects they would normally avoid. They became “hyper-oral,” meaning they would put anything and everything in their mouth. They also became hypersexual. A similar syndrome occurs in humans. The patient I encountered that night had an infection affecting parts of her brain analogous to those parts in monkeys that Paul Bucy removed. All the cultural and neural machinery that puts a check on such behavior was dissolved  by her infection.  She displayed  sexual desire, the deep-rooted instinct that ensures the survival of our species, in its most uninhibited form.

People are preoccupied by sex. In an American national survey from the mid-1990s, over half the men and a fifth of the women reported thinking about sex at least once a day. In an earlier survey from the 1970s, people were called at different times of the day and asked if they had thought of sex in the last 5 minutes. For people between 26 and 55, 26% of men and 14% of women said yes. Sex sells. Pornography is one area that has not had trouble  surviving commercially on the Internet. By some accounts, over $3,000 are spent every second on Web-based pornography. Lest you think this propensity is a peculiarly  human obsession, it turns out that male rhesus monkeys also watch pornography. Researchers at Duke University found that male monkeys choose to watch pictures of aroused female monkey behinds even if it means foregoing juice rewards. As an aside, they also look a lot at high-status males. Our preoccupation with sex and power is built into the hardware of our simian brains.

We can think of sex as a play with different acts. The first act is desire, the next one is sexual stimulation and pleasure, and the final act is the aftermath, the languorous glow of the sexually sated. Most of what we know about how the brain responds in these acts comes from studies of young heterosexual men. These specimens are found in abundance on college campuses and are quite willing to volunteer for sex studies.

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