Mounting evidence suggests that there are multiple pathways to orgasm for women, but not all researchers are convinced.

It's a debate that's been running since at least the days of Sigmund Freud: Can women climax from vaginal stimulation alone? And is there any difference between so-called clitoral and vaginal orgasms?

Now, a new series of essays lays out the evidence that vaginal and clitoral orgasms are, in fact, separate phenomena, activating different areas of the brain and perhaps revealing key psychological differences between women.

"We have plenty of evidence regarding the difference between the two main orgasms, clitoral and vaginally activated orgasm," said Emmanuele Jannini, a professor of endocrinology at the University of Aquila in Italy. Jannini organized and contributed to the essay series, published online March 28 in the Journal of Sexual Medicine.

Evidence for orgasms

Arguably, unraveling the mystery of whether vaginal orgasms exist should be simple: Ask women if they have them. But in practice, it's a bit harder to tease out the exact sexual stimulation that leads to orgasm. [Sex Quiz: Myths, Taboos & Bizarre Facts]

French gynecologist Odile Buisson argues in her Journal of Sexual Medicine essay, for example, that the front wall of the vagina is inextricably linked with the internal parts of the clitoris; stimulating the vagina without activating the clitoris may be next to impossible. Thus, "vaginal" orgasms could be clitoral orgasms by another name.

Other research, however, would tend to suggest two distinct types of female orgasm. Barry Komisaruk of Rutgers University has conducted multiple studies in which women masturbate while having their brains scanned with a functional magnetic resonance imaging (fMRI) machine. The results show which sensory brain areas activate in response to stimulation.

"If the vagina stimulation is simply working via clitoral stimulations, then vaginal stimulation and clitoral stimulation should activate the exact same place in the sensory cortex," Komisaruk told LiveScience. "But they don't."

In fact, Komisaruk reports in the journal, the brain areas for clitoral, cervical and vaginal stimulation cluster together but only overlap slightly, like a "cluster of grapes."

And then there is other evidence for multiple types of orgasms: Women report that vaginal and clitoral orgasms feel different. Women with spinal cord injury that cuts off all communication between the clitoris and the brain can still have orgasms with vaginal stimulation. Some lucky ladies can even "think" themselves to orgasm with no stimulation at all. (There are also reports of women orgasming from tough abdominal workouts at the gym.)

"[O]rgasm in women is in the brain, it is felt in many body regions, and it can be stimulated from many body regions as well as from imagery alone," wrote Rutgers University professor emerita Beverly Whipple, one of the discovers of the also-controversial "G-spot," an area on the front vaginal wall that may be particularly sensitive to sexual stimulation.

The meaning of an orgasm

If the origin of the orgasm is controversial, so, too, is the purpose of this reflex. Whipple's research has suggested that the sensitive G-spot has a pain-blocking function during labor; when the baby's head is stretching out the vaginal walls, it might be advantageous to have a little relief. Her studies have found that when pressure is applied to the G-spot, a woman's pain threshold shoots up 47 percent. In other words, it takes a lot more pain before the woman says "ouch."

If the G-spot stimulation is pleasurable, Whipple and her colleagues found, the pain threshold increases by 84 percent compared with no stimulation, and during orgasm, that threshold hits a whopping 107 percent.

Most provocatively, some research links vaginal-only orgasms with both physical and mental health. The research is correlational, so it's not entirely clear whether healthier women are prone to vaginal orgasms, whether vaginal orgasms somehow promote health, or whether some unknown factor links the two.

For instance, one study found women who have vaginal orgasms have a lower resting heart rate than those who don't. Other research has found women who orgasm without clitoral stimulation are less likely on average to use certain maladaptive psychological coping mechanisms, said Stuart Brody, a psychologist at the University of West Scotland who has conducted this research. Among these mechanisms are somatization (psychological symptoms manifesting as physical complaints), displacement (displacing an emotion about one person or object onto another), and isolation of affect (disconnecting emotions from experiences).

"Impairment of specifically vaginal orgasm is associated with a variety of other psychological impairments," Brody told LiveScience. The findings aren't meant as a value judgment on women who don't experience vaginal orgasms, he said. But given that some research suggests teaching women that orgasms originate only with the clitoris results in fewer vaginal-only orgasms, Brody argues that this kind of anti-vaginal sex advice could count as "malpractice." [5 Myths About Women's Bodies]

Busting myths

Brody's data is strong, Rutgers' Komisaruk said, though he is a controversial figure in the field given his emphatic interpretations of the benefits of vaginal orgasms.

But one orgasm myth that all researchers agree should be kicked out of the bedroom is that the vagina is insensitive. This idea started spreading due to early sexologist Alfred Kinsey, who reported that women failed to respond to the sensation of a cotton wisp rubbed along their vaginal walls.

But Kinsey's own data shows that more than 90 percent of the women felt it when pressure was applied to their vaginal walls, Komisaruk said. Somehow, that fact fell by the wayside, and Kinsey and company sparked the misconception that the vagina and cervix have no feeling at all.

New fMRI studies and more sophisticated understandings of anatomy are unraveling what Jannini called a woman's "very complicated machinery." Nonetheless, Jannini cautioned, women who don't orgasm vaginally should not feel inferior.

"A woman should have an understanding — who is she, how is her body composed, what is the possibility of her body, but she should not be looking for something like a race, like a game, like a duty," Jannini said. "Looking for the G-spot orgasm or the vaginal orgasm as a need, as a duty, is the best way to lose the happiness of sex."

You can follow LiveScience senior writer Stephanie Pappas on Twitter @sipappas. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.