Carnal Knowledge: They give pleasure; science asks why

There are some natural phenomena whose wonder only deepens upon scientific investigation.

Take the orgasm. Scientists know it involves muscle contractions. They know it makes your pupils expand, and heart rate and blood pressure surge.

But why do orgasms feel good?

I was surprised to find that this is still something of a scientific mystery - though one that a few intrepid researchers are just starting to unravel.

"Really and truly, people don't know," says Julia Heiman, director of the Kinsey Institute for Sex Research and coauthor of

Becoming Orgasmic

.

Right now, says Heiman, there's a big debate over how the female orgasm evolved. Researchers would also like to know just how different the female kind is from the male.

"Why is it easier for women to have multiple orgasms than it is for men?" Heiman asks. "How does it interact with attachment issues?"

There are lots of other questions, she says, but oddly, in our supposedly sex-obsessed society, it's nearly impossible to get funding for sex research.

Another complication: The orgasm question touches on some profound mysteries about how feelings and consciousness can emerge from the brain.

For Barry Komisaruk of Rutgers University, that's what makes the neurobiology of orgasm so fascinating. A coauthor of the semi-technical 2006 book

The Science of Orgasm

, he got interested in applying his field of neuroscience to sex while studying rats.

Observing that vaginal stimulation caused a cascade of hormonal changes and kicked in a painkilling effect more powerful than morphine, Komisaruk reasoned that decoding the neurobiology of female rat sex might lead to a blockbuster drug for humans.

He never found that drug but the work did lead to the discovery that the electrical impulses needed for orgasm travel outside the spinal column, through what is known as the vagus nerve.

This explained why some people with complete spinal cord injury can lose all sensation from below the waist yet still have orgasms - sometimes through sex, and sometimes through stimulation of the chest or neck, where they can still feel.

But what happens once the signal arrives in the brain?

To get at that, Komisaruk started putting women into the decidedly non-romantic confines of a functional MRI - a machine similar to a regular MRI but designed to map the brain in action - and asking them to bring themselves to orgasm.

He was surprised to discover that orgasm activated the same areas of the brain that respond to pain - the anterior cingulate cortex and the insula.

Other neuroscientists have suggested that the cingulate controls the subjective feeling of pain or pleasure, while a different part controls the sensation. One researcher, for example, noted that a patient with cingulate lesions could still identify the location of the pain but no longer minded it.

Perhaps less of a surprise was Komisaruk's finding that orgasm acts chemically in the brain by sending the messenger dopamine from a region in the back to the front, where it triggers a reaction a bit like those inspired by nicotine or cocaine.

This pain-pleasure connection might also relate to a medical mystery Komisaruk has begun investigating. Some women, he says, feel like they're constantly on (or over) the edge of an orgasm - but instead of pleasure, many feel discomfort, annoyance or even pain. The condition, called Persistent Sexual Arousal Syndrome, has only recently been recognized.

Komisaruk's lab has also studied the brains of women who say they can bring themselves to orgasm with thought alone. For some it's a sexual thought that does the trick, he says, but for others it's more abstract - something that has to do with focusing energy.

In the scanner, their brains typically showed the same patterns as those of women having conventional orgasms.

While this is all fascinating and potentially useful, Komisaruk says, he always runs up against a wall that no one researcher, or even field of research, seems able to break through. So he's joining other psychologists, neuroscientists and philosophers to try to tackle one of the most profound mysteries of life: How does the transport of chemicals and electrical impulses in the brain add up to subjective feelings - and, ultimately, to consciousness itself?

What, exactly, is pleasure?