How, for example, can they explain the fact that some men and women who are paralyzed and numb below the waist are able to have orgasms?
How to explain the "orgasmic auras" that can descend at the onset of epileptic seizures -- sensations so pleasurable they prompt some patients to refuse antiseizure medication?
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And how on Earth to explain the case of the amputee who felt his orgasms centered in that missing foot?
No one -- no sexologist, no neuroscientist -- really knows. For a subject with so many armchair experts, the human orgasm is remarkably mysterious.
But today, a few scientists are making real progress -- in part because they're changing their focus. To uncover the orgasm's secrets, researchers are looking beyond the clitoris, vagina, penis and prostate, to the place behind the scenes where the true magic happens. They're examining the central nervous system: the network of electrical impulses that zip to and fro through the brain and spinal cord.
In an orgasm orchestra, the genitalia may be the instruments, but the central nervous system is the conductor.
Armed with new lab tools and fearless volunteers, scientists are getting first-ever glimpses of how the brain lights up (and, in places, shuts down) when the orgasmic fireworks go off. They're tracing nerves and finding new pathways for pleasure that help explain how people with shattered spinal cords can defy sexual expectations.
A few labs are even tinkering with devices that could put patients directly in touch with their orgasmic abilities by letting them observe their sexual brain patterns and "train" themselves to find the elusive frisson, or (in something akin to the Orgasmatron in Woody Allen's 1973 movie "Sleeper") letting them zap a sweet spot in their spinal cord with toe-curling electrical pulses.
"There's a tremendous amount we don't know about orgasms," says Barry R. Komisaruk, psychology professor at Rutgers University and coauthor of the 2006 book "The Science of Orgasm." "But we're on the verge of getting a lot of very important information and really understanding what to do with it."
It's not just the pleasure principle driving this research, says Julia R. Heiman, director of the Kinsey Institute, a nonprofit organization at Indiana University. Sex is an important part of human relationships, she says, which in turn can affect psychological health. "An awful lot of illness, or treatments for illnesses, interfere with people's orgasms," she says, including multiple sclerosis, cancer, Parkinson's disease, depression and diabetes.
Indeed, if surveys are to be believed, this most delightful of experiences is elusive for many. About 43% of women and 31% of men in the U.S. between ages 18 and 60 meet criteria for sexual dysfunctions, according to a 1999 report on the sexual behavior of more than 3,000 U.S. adults.
Orgasm researchers hope their efforts will help some of these people -- eventually. For now, reports are more likely to include the words "parasympathetic nervous system" than "try this at home tonight."
A difficult subject
It has never been easy to study any aspect of sexuality, let alone one so erotically center-stage as an orgasm. "Almost everybody is interested in orgasms, but it is also very difficult to start this kind of work," especially in the U.S., says Dr. Gert Holstege, a neurologist at University of Groningen in the Netherlands. "The Victorian time is still not over."
So it's not surprising that some of the most impressive discoveries in the field of orgasm science were stumbled upon by accident. For example, Viagra originally was a drug being tested for treatment of high blood pressure and heart disease.
Other touted aids lack formal proof. No doubt most of the nostrums available from pharmacies or the Internet derive their power from the "oh-please-please-make-this-work" power of the placebo effect.
And though sexologists as far back as Alfred Kinsey have tallied people's orgasmic habits in exquisite detail, only now are researchers beginning to understand how it all works.
Orgasms are difficult to define, let alone reverse-engineer. A few blueprints, however, have already been sketched out. First, stimulating the genitals sends electrical impulses along three main paths -- the pelvic, hypogastric and pudendal nerves. Next, these titillating signals enter the spinal cord at the base of the spine and zip up to brain regions that respond to genital sensations.
Then other parts of the brain leap into action. Some send signals back down to the body with certain instructions -- lubricate the vagina, stiffen the penis, pump blood harder, breathe faster.
The intensity builds to a crescendo, and just like a long-awaited sneeze, tension is released in an explosive rush. The heart rate doubles. In women, the uterus contracts rhythmically; in men, sperm-carrying semen is propelled out of the body.
And somehow, by mechanisms not yet understood, the brain perceives all this activity as a darn good feeling.
Such a signaling pathway would seem to rule out orgasms for anyone whose spinal cord is completely severed, because people with such injuries cannot feel the brush of a finger across the penis or clitoris.
But about two decades ago, anecdotal evidence started accumulating to the contrary. This was as a bit of a surprise to the medical profession, which for decades had told patients with damaged spinal cords to give up hope of a sex life. Researchers began to investigate.
One, Dr. Marca Sipski-Alexander, published studies in 2001 and 2006 reporting that about 50% of 45 men and 44% of 68 women -- all with varying locations and degrees of spinal cord injury -- had orgasms in the lab, with the help of adult videos and genital stimulation by hand or vibrator.
The findings show that the normal genitals-to-spine-to-brain route for an orgasm is not the only one. The best explanation may be that a touch unperceived by the brain can still be doing its work, says Alexander, a rehabilitation medicine professor at the University of Alabama at Birmingham School of Medicine.
Alexander thinks that an orgasm, like urination, is a reflex. Both functions can be controlled partly by willpower. But just as voiding your bladder doesn't require the say-so of your higher brain, she says, maybe orgasms don't either. Maybe all that's needed is some chit-chat between pelvis and spinal cord.
Some studies, mostly in animals, support this line of thought. In the brain stem and spinal cord, researchers have found hard-wired programs -- clusters of cells acting as primitive mini-brains of sorts -- that produce rhythmic movement without any higher brain input. These so-called central pattern generators are what let mollusks swim, rats crawl, tadpoles breathe and perhaps human males thrust their pelvises and ejaculate. Rat studies suggest that females, too, have these muscle-contracting proto-brains.
But orgasms are more than just muscular contractions. They feel good. So how do the brains of spinal-cord-injured people sense the pleasure? "I don't know. No one knows that yet," Alexander says.
An alternate route
Rutgers University's Komisaruk and retired Rutgers professor Beverly Whipple, coauthor of "The Science of Orgasm" and "The G Spot and Other Discoveries About Human Sexuality," believe they do know. But they don't think an orgasm is a reflex. Through studies of spinal-cord-injured women, they've found evidence of what appears to be a new orgasmic pathway, one that bypasses the spine completely.
The proposed detour makes use of a vast highway of nerves called the vagus nerve network. Like the vagabonds for which they were named, vagus nerves wander throughout the body. They start at the base of the brain, slide down the neck (but not the spinal cord) and stretch to all the major organs, and (at least in female rats) to the uterus and cervix. If vagus nerves reach human pelvises, genital signals could hopscotch over the spinal cord and still reach the brain.
Animal experiments support the idea. Female rats with intact vagus nerves but snipped genital nerves (cutting off their signals to the spinal cord) still respond to vaginal stimulation in their normal, albeit rodent-like, fashion: enlarged pupils, rapt attention and a tendency to ignore painful stimuli applied to their paws. But when the vagus nerves in the pelvises are also severed, all these sexual responses stop.
To investigate further, in a 2004 study, Komisaruk and Whipple worked with four women with shattered spinal cords. Each stimulated her cervix with a phallus while the researchers used fMRI scanning to measure brain activity.
Despite their severed spinal cords, all women reported feeling the touch of the stimulator, Whipple says. The sensation at the cervix was reaching the brain. What's more, in the fMRI scans their brains lighted up in an area where vagus nerve signals are processed. And three of the volunteers experienced an orgasm.
Komisaruk and Whipple have compared these brain images with those of women who are able to have orgasms by thought alone (who thus provide a clean brain image of a person reaching climax).
They found that orgasms elicit strong activity in the nucleus accumbens, the reward center, which also lights up in response to nicotine, chocolate, cocaine and music; in the cerebellum, which helps coordinate muscle tension; and parts of the hypothalamus, which releases oxytocin, the trust and social-bonding hormone.
Intriguingly, areas of the cortex that respond to pain also responded during orgasm. "Perhaps it's related to the fact that people often have pained expressions at the time of orgasm," Komisaruk says.
The amygdala, the brain's emotional center, and the hippocampus, which deals with memory, light up too. This helps explain a medical mystery: When epileptic seizures start in these areas, the electrical frenzy can triggers euphoric feelings called orgasmic auras.
Most patients find the experience displeasing. But in one published case, a 51-year-old woman said her auras were so pleasant she wouldn't consider antiepileptic drugs or surgery.
Role of inactive regions
Holstege's group has also studied the sexually stimulated brain, and his findings suggest that orgasms are not just about how the brain lights up but also about where it shuts off.
In the late 1990s, his team recruited volunteers plus their sexual partners, who would stimulate them in the lab.
To measure brain activity, the researchers used PET scanners, which require obsessive attention to timing. The stimulators were asked to induce an orgasm in their receivers within a two-minute window, with an eight-minute advance warning. (Couples were told to practice at home first.)
Results from men and women were fairly similar, says Janniko R. Georgiadis, a neuroscientist at the University of Groningen and a study coauthor. There were several regions of activation, but the most striking result, Georgiadis says, was how certain regions in the front of the brain shut down during orgasm, especially one just behind the left eyeball. Researchers have long noticed that damage to this area -- the lateral orbitofrontal cortex -- can leave people with wildly antisocial and impulsive tendencies, including hypersexuality.
Shutdowns in the brain's prefrontal cortex appears crucial, Georgiadis adds. "It's the seat of reason and behavioral control. But when you have an orgasm, you lose control."
Regions called the temporal lobes also showed damped activity. In fact, the less activity these regions showed, the more sexually aroused the women felt. These deactivations might explain the appeal of autoerotic asphyxiation, the researchers say. Depriving a brain of blood during sex not only provides a dangerous thrill but also shuts down key brain regions, leading to addictive orgasmic euphorias.
Unsticking the brain
Back in New Jersey, Komisaruk is trying to apply some of this new brain knowledge. He is studying two extremes: women who complain of constant sexual arousal and find no relief in orgasms and those who can never have an orgasm. He hopes to reveal where their brains are "stuck" and help them alter their brain patterns.
The setup is simple: Women lying in an MRI scanner watch a computer display of their brain activity. Scans of women with persistent genital arousal disorder reveal unusually high activation in regions that respond to genital stimulation. It shows, Komisaruk says, that the women's complaints are real. Their brain thinks the genitals are constantly being stimulated.
Komisaruk is coaching them to use neuro-feedback -- mental strategies such as counting or imagery -- to alter their brain activity. If they see those genital brain regions cooling seconds after their mental exercises, they can refine their techniques and eventually do it without the scanner, whenever these brain areas again slip into hyperdrive.
Fire rather than ice might be the trick for anorgasmic women, whom Komisaruk plans to study next. For some women, clitoral stimulation might travel along the spinal cord but then is somehow blocked so they don't travel to the brain regions they need to.
"We want to see if there's a blockage somewhere and if that blockage is susceptible to a change in mental activity," he says. Anorgasmic women might practice in a lab with a vibrator, trying to mimic other women's successful brain patterns.
The brain is surprisingly plastic, Komisaruk says. Witness the curious case -- described by UC San Diego neuroscientist Dr. V.S. Ramachandran -- of the man who had orgasms in his phantom foot.
When the man's foot was amputated, cells in the "foot" part of the brain were suddenly deprived of stimulation. They died, leaving prime cerebral real estate vacant.
Then, like an opportunistic roommate, a neighboring region in the man's brain likely sent sprouts to commandeer the vacated landscape. That region? One that processes input from penis and vulva.
The result: The man felt foot-sized orgasms in a foot he no longer had.
Nothing quite so drastic is expected to occur with a bit of orgasmic neural training in the lab, Komisaruk says. But the anecdote points out that the brain is indeed capable of some very imaginative tricks.