Spontaneous orgasms are rather like volcanic eruptions: there’s rarely a convenient time for one to occur, and once something has triggered it there’s no way of stopping the flow. Fortunately, the human body’s naughty buttons are very well sign-posted, so it’s usually pretty easy to avoid any unwanted excitement. However, there are some strange stimuli out there that can scramble your libido, causing you to get your rocks off when you least expect it.

As the name suggests, anti-depressants are designed to improve mood, but some can apparently make you a little too happy. Perhaps the most spectacular side effect ever observed was produced by a drug called clomipramine, which caused some patients to orgasm every time they yawned.

It’s not known how this depression medication generated such an outrageous off-target consequence, but it may have something to do with the adrenocorticotropic hormone, which plays a role in inducing yawning and is also involved in male ejaculation.

Barry Komisaruk is a neurologist at Rutgers University and an expert on non-genital orgasms. He told IFLScience that orgasms represent a generalized process within the nervous system, whereby “stimuli of various types build up and reach an intensity that can trigger a high-threshold system.”

Similarly, he said that “yawning and stretching represent the same kind of orgasmic process of a build-up of excitation – in this case, muscle tension – which then triggers a relaxation. The question is, how can other types of stimuli cross into the pleasurable aspect of orgasm? And I don’t think anybody has a good explanation of that.”

Another anti-depressant called venlafaxine can sometimes produce persistent genital arousal disorder (PGAD) in women when they stop using it. In one study, a woman reported being unable to ride in a car after discontinuing the medication, as the vibrations caused her to become aroused and experience up to a dozen orgasms, one after the other.

PGAD is characterized by frequent genital arousal in the absence of any sexual arousal or desire. The cause of the condition is not known, but several unexpected factors have been found to contribute to it. In one case, a woman began to experience up to 15 orgasms a day after increasing the amount of soy in her diet to 1.8 kilograms (4 pounds) a day.

David Goldmeier, head of the Jane Wadsworth Sexual Function Clinic at St Mary's Hospital in London, told IFLScience that there are two types of PGAD. The most common form is caused by a pudendal neuralgia, whereby the pudendal nerve fires when it shouldn't. "And because it takes sensory information from the genital area, it gives information at the cerebral level that the person is genitally aroused, even if they aren’t sexually aroused," he explained.

The other type of PGAD occurs when people are not able to mentally disregard any unwanted genital stimulation they may experience as they go about their day, so that "they become cognitively focussed on it, and the anxiety perpetuates the arousal."

In both cases, Goldmeier claims that the condition "can be pretty devastating in terms of the psychological sequelae."

Spontaneous orgasms and volcanic eruptions have a lot in common. Pixabay

Everyone knows where you’re supposed to touch yourself if you want an orgasm, so we needn’t spell it out. But sometimes the brain can get its wires crossed and start mistaking an innocent part of the body for the fun parts.

A middle-aged Dutch woman once made it into the scientific journals when, shortly after coming out of a coma, she began experiencing spontaneous orgasms that originated in her left foot.

Researchers were even able to bring her to orgasm by electrically stimulating her foot, and suggested that her brain had somehow lost the ability to differentiate between her foot and her vagina, as the nerves from both body parts enter the spinal cord at more or less the same point.

It’s events like this that illustrate just how much neuroscience goes into every orgasm, and how small discrepancies can make the difference between perfect control and sexual incontinence.

For example, Komisaruk explained how “the representation of the foot in the sensory cortex is adjacent to the genital representation,” and that if a foot is amputated or the nerves in it become in some way scrambled, then there may be some “sprouting from the input to the genitals to the neurons that used to respond to the foot,” leading to some very peculiar sensations in some rather unexpected places.

Among the many brain regions that become activated during an orgasm are the hippocampus, cerebellum, lower brainstem, and the frontal cortex. A malfunction in any of these areas can lead to some seriously weird erotic episodes, as one epileptic woman discovered when she started having orgasms during seizures that were induced exclusively by the act of brushing her teeth. Brain scans revealed that this may have been caused by a damaged hippocampus.

Yet the brain’s sexual quirks can also be taken advantage of in order to gain greater control over one’s orgasms. When a psychologist named Rafe Biggs became paralyzed from the chest down after falling off a roof, he was able to rewire his nervous system so that he could experience orgasms through stimulating his thumb, rather than his now-obsolete penis.

This sexual re-incarnation was made possible by the brain’s neural plasticity, whereby new neurological pathways can be created through repeated activation. In this case, Biggs managed to retrain his brain to associate sexual pleasure with a different part of the body, achieving what is known as a "transfer orgasm".

Sometimes the brain confuses other body parts for the genitals, leading to some very inconvenient orgasms. Designed by Chevanon / Freepik

Experiencing sexual arousal while working out is a surprisingly common occurrence, and a recent survey of 370 women who claimed to have got the horn at the gym revealed that abdominal exercises like crunches and sit-ups are the most likely to produce an orgasm.

Of all the respondents who admitted having climaxed during a workout, 45 percent said that core exercises had been the culprit, while smaller numbers claimed to have orgasmed as a result of weight-lifting and climbing.

True to its reputation, the female orgasm remains shrouded in mystery, and no one is exactly sure what causes these "coregasms", although it may have something to do with pressure on the clitoris or increased blood flow to the vagina.

Core exercises can have the double benefit of strengthening your abs and giving you an orgasm. Pixabay

But perhaps the strangest orgasm of all is that produced by sniffing a foul-smelling fungus called a netted stinkhorn, which grows on the lava fields of Hawaii. According to one study, around half of all women who catch a whiff of this pongy mushroom experience a sudden explosion of sexual pleasure, while men are completely immune to its charms. 

No explanation for this phenomenon has been given, and the claims made by this study have been disputed, so if you’re looking for a good time, sifting through lava probably isn’t the best way to go about it.

Plus, having a spontaneous orgasm in the middle of a volcanic eruption would be doubly inconvenient.