What happens in the brain during an orgasm?

Although the reasons for having sex of any kind are varied and complex, reaching orgasm is usually the goal. Because we're all so different, coming up with a universal description of an orgasm is impossible. The one thing that most people can agree on is that it's an incredibly, intensely pleasurable experience.

So what is it? When in doubt, go to the dictionary. The Oxford English Dictonary defines an orgasm as "a sudden movement, spasm, contraction, or convulsion [...] a surge of sexual excitement." Merriam-Webster gets more descriptive, stating that it's "an explosive discharge of neuromuscular tensions at the height of sexual arousal that is usually accompanied by the ejaculation of semen in the male and by vaginal contractions in the female." The famous sex researcher Dr. Alfred Kinsey once said that an orgasm "can be likened to the crescendo, climax, and sudden stillness achieved by an orchestra of human emotions ... an explosion of tensions, and to sneezing" [source:Geddes].

Dr. ­Kinsey's comparison to sneezing might be debatable, but other than that, all of these definitions are basically correct. They're just a few of the many different attempts to describe exactly what it means to have an orgasm.

Nearly every aspect of the orgasm -- what's required to have one, why some people can't seem to achieve one, why we have them at all -- has been the subject of much research and debate. What happens to the body during an orgasm is pretty well-known, and it's no surprise that the brain plays a big part in reaching one. But researchers are still in the process of figuring out exactly what's happening in the brain during an orgasm. Let's start with looking at the messages that the body sends to the brain.

Orgasms and Nerves

Without nerves sending impulses back to the spinal cord and brain, an orgasm wouldn't be possible. Just like any other area of the body, the genitalia contain different nerves that send information to the brain to tell it about the sensation that's being experienced. This helps to explain why the sensations are perceived differently depending on where someone is being touched. A clitoral orgasm, for example, differs from a vaginal orgasm because different sets of nerves are involved.

All of the genitalia contain a huge number of nerve endings (the clitoris alone has more than 8,000 of them), which are, in turn, connected to large nerves that run up through the body to the spinal cord. (The exception is the vagus nerve, which bypasses the spinal cord.) They perform many other functions in the body in addition to providing the nerve supply, and therefore feedback to the brain, during sexual stimulation. Here are the nerves and their corresponding genital areas

• hypogastric nerve - transmits from the uterus and the cervix in women and from theprostate in men
• pelvic nerve - transmits from the vagina and cervix in women and from the rectum in both sexes
• pudendal nerve - transmits from the clitoris in women and from the scrotum and penis in men
• vagus nerve - transmits from the cervix, uterus and vagina

The role of the vagus nerve in orgasms is a new discovery and there's still much that's unknown about it; until recently, researchers didn't know that it passed through the pelvic region at all.

Since most of those nerves are associated with the spinal cord, it would stand to reason that a person with a severed spinal cord wouldn't be able to have an orgasm. And for a very long time, that's what people with these types of injuries were told. However, recent studies show that people with spinal cord injuries -- even parapalegics -- can reach orgasm. Dr. Barry Komisaruk and Dr. Beverly Whipple of Rutgers University conducted a study on women with severed spinal cords in 2004. They discovered that these women could feel stimulation of their cervixes and even reach orgasm, although there was no way their brain could be receiving information from the hypogastric or pelvic nerves. How was this possible? An MRI scan of the women's brains showed that the region corresponding to signals from the vagus nerve was active. Because the vagus bypasses the spinal cord, the women were still able to feel cervical stimulation.

So during sexual stimulation and orgasm, different areas of the brain receive all of this information that lets it know exactly what's happening -- and that what's happening is very enjoyable. But until recently, we had no way of knowing exactly what was happening in the brain at the exact moment of orgasm. We'll check out the latest research next.

Pleasure Center of the Brain: Light It Up

You may have heard that the brain has a pleasure center that lets us know when something is enjoyable and reinforces the desire for us to perform the same pleasurable action again. This is also called the reward circuit, which includes all kinds of pleasure, from sex tolaughter to certain types ofdrug use. Some of the brain areas impacted by pleasure include:

• amygdala - regulates emotions
• nucleus accumbens - controls the release of dopamine
• ventral tegmental area (VTA) - actually releases the dopamine
• cerebellum - controls muscle function
• pituitary gland - releases beta-endorphins, which decrease pain; oxytocin, which increases feelings of trust; and vasopressin, which increases bonding

Although scientists have long been studying the pleasure center, there hadn't been much research about how it relates to sexual pleasure, especially in women. In the late 1990s and the mid-2000s, a team of scientists at the University of Groningen in the Netherlands conducted several studies of both men and women to determine brain activity during sexual stimulation. The team used PET scans to illustrate the different areas of the brain that would light up and shut off during sexual activity. In all of the tests, the subjects were scanned while resting, while being sexually stimulated and while having an orgasm.

Interestingly, they discovered that there aren't too many differences between men's and women's brains when it comes to sex. In both, the brain region behind the left eye, called the lateral orbitofrontal cortex, shuts down during orgasm. Janniko R. Georgiadis, one of the researchers, said, "It's the seat of reason and behavioral control. But when you have an orgasm, you lose control" [source: LA Times]. Dr. Gert Holstege stated that the brain during an orgasm looks much like the brain of a person taking heroin. He stated that "95 percent is the same" [source: Science News].

There are some differences, however. When a woman has sex, a part of the brain stem called the periaqueductal gray (PAG) is activated. The PAG controls the "flight or fight" response. Women's brains also showed decreased activity in the amygdala and hippocampus, which deal with fear and anxiety. The team theorized that these differences existed because women have more of a need to feel safe and relaxed in order to enjoy sex. In addition, the area of the cortex associated with pain was activated in women, which shows that there is a distinct connection between pain and pleasure.

The studies also showed that although women m­ay be able to fool their partners into thinking they've had an orgasm, their brains show the truth. When asked to fake an orgasm, the women's brain activity increased in the cerebellum and other areas related to controlling movement. The scans didn't show the same brain activity of a woman during an actual orgasm.

But what about people who can't reach orgasm at all?

Neither Here Nor There: Anorgasmia and Non-genital Orgasms

I­n some cases, we know what causes anorgasmia(the inability to reach orgasm). Drugs like Celexa, Zoloft and Paxil -- known as SSRIs, or selective seratonin reuptake inhibitors -- are often used to treat depression, anxiety and other mental illnesses. Like most drugs, however, they can have side effects. For some people, this includes sexual ones, including anorgasmia. But why? SSRIs can decrease the brain's production of dopamine, the neurotransmitter that provides pleasurable feelings and reinforces a person's desire to once again perform the action that brought him or her pleasure. Sometimes the problem goes away on its own, or it can be resolved by switching to a different antidepressant or taking another drug in addition to the SSRI. However, a small number of people experience post-SSRI sexual dysfunction (PSSD) that lasts for days, weeks, months or even years after discontinuing use of an SSRI. The cause of this dysfunction isn't understood, as stopping the SSRI allows dopamine production to return to normal.

The Dutch studies about orgasms (mentioned earlier), along with others, have also been the basis for continuing research in helping women who are anorgasmic. Dr. Barry Komisaruk at Rutgers University is currently studying women who are anorgasmic and women who are constantly aroused sexually but are unable to reach orgasm. The latter group of women were each put in an MRI scanner where they could see their brain activity on a monitor. Their brain scans showed that the brain thought they were in fact constantly being sexually stimulated. The women then used imagery and other neurofeedback exercises to calm their brains. Dr. Komisaruk believes that anorgasmic women could also learn to read and react to their brain activity to try to reach orgasm.

Perhaps more unusual-sounding than orgasmia is the concept of orgasms that have nothing to do with the genitalia at all. Some people can orgasm from being touched in other places on the body, such as the nipples. In this case, researchers believe that the sensations in the nipples are transmitted to the same areas of the brain that receive information from the genitals. However, people have also reported actually feeling orgasms in other parts of their bodies, including their hands and feet. Several people have even described having orgasms in limbs that were no longer there. One reason may be the layout of the cortical homunculus, a map that shows how different places of the brain's sensory and motor cortices correspond to the organs and limbs of the body. A person who feels an orgasm in a phantom foot, for example, may have experienced a remapping of the senses because the foot is located next to the genitals in the homunculus. The foot is no longer there to provide sensation, so the area for genital sensation took over the space.

Although we now know more about how orgasms impact the brain than ever before, there's still a lot that we don't know. For example, scientists are still debating the evolutionary reason behind the female orgasm. But it's probably safe to say that most people aren't too concerned about the "why" -- they'd prefer to focus on the whos, whats and whens of sex.