The Belfast Telegraph reports on work done by a team of scientists who were the first to watch the brain in action during orgasm.
Barry R. Komisaruk, Carlos Beyer-Flores and Beverly Whipple scanned the brains of women with spinal cord injuries as they masturbated. It's been thought that because such injuries cut off feeling to the lower part of the body, these people would not be able to feel anything from sex, either.
(I'm not sure why doctors thought that, since there is plenty of anecdotal information about male paraplegics and quadriplegics being able to enjoy genital sex and ejaculation in the absence of feeling in the lower half of their bodies. Whatever.)
In any case, the scientists found that these women could orgasm -- and some of the women were thrilled to discover this as well, because they'd believed their doctors and had never tried masturbation or sex since their injuries.
The scans showed that orgasm involves many parts of the body and brain. In the brain, the reward and oxytocin systems were activated.
One part of the brain that was strongly activated was the nucleus accumbens, which other scientists have shown becomes activated by psychoactive drugs such as cocaine, nicotine and caffeine. Another two areas were the insula and anterior cingulate, which become active in response to pain. "It suggests there is some sort of inhibitory activity going on there, as orgasm and vaginal stimulation are strong pain-blocking stimuli." The third area of interest was the paraventricular nucleus, where the hormone oxytocin is produced. Oxytocin is released into the blood stream at orgasm and causes uterine contractions.
What is very interesting and new is that the scientists found an alternate neural pathway from the vagina and cervix to the brain: the vagus nerve. From the article:
the vagus nerve, which leads from the lowest part of the brainstem, the medulla, through the base of the skull, down the neck, into the chest cavity, through the diaphragm and into the abdominal cavity without using the spinal cord. The first evidence that the nerve goes to the pelvic region was found in 1990 with rats. At this stage, however, it was not known whether it reached the same region in humans.
They do know that the vagus nerve is involved in feelings of satiety after eating. As the gut digests fat, it releases CKK, which travels up the vagus nerve to the brain, stimulating it to release oxytocin, which then travels back down the vagus nerve to tell the body it's had enough to eat.
This research, therefore, is another clue to the question of why people -- especially women -- eat when they're lonely. Eating activates the same neural pathways and oxytocin responses as sex.