2-Minute Neuroscience: Vestibulocochlear Nerve (Cranial Nerve VIII)

The vestibulocochlear nerve (cranial nerve VIII) is responsible for carrying information to the brain from the vestibular system and the cochlea. The information from the cochlea deals with hearing, while the information from the vestibular system deals with vestibular sensations, which include information about head position and movement. These vestibular sensations enable us to keep our balance, stabilize our head and body during movement, and maintain posture. In this video, I discuss the anatomy and function of the vestibulocochlear nerve, as well as what symptoms can appear when the nerve is damaged.

The mysterious dancing mania and mass psychogenic illness

Try to imagine yourself walking along the streets of a city (maybe the one you live in, or one you’ve visited, or one you simply make up in your head—as long as you can picture it clearly it doesn’t matter much). Think of the shops and businesses you might pass as you stroll down the sidewalk, the smells of food emanating from nearby restaurants, and the noises you’d hear—intermittent car horns, snippets of conversation, the discordant sounds of construction equipment. Now, imagine you approach a street corner, and as you do you begin to hear some rhythmic music playing from just out of view—on what sounds like bagpipes (to really set the mood, click play on the video below for some appropriate background music). As you turn the corner, curious to find the source of the music, you see a large city park. It charmingly interrupts the asphalt and concrete of the city with expansive green grasses, dense leafy trees, and a bubbling decorative fountain. But despite its beauty, the park is also the backdrop to one of the strangest spectacles you’ve ever witnessed.

The park is filled with people—perhaps a hundred, maybe more. Many of them are naked. Others are wearing clothes that are dirty, ripped, and often hanging loosely from their undernourished bodies. A large group of them have formed a circle by holding hands, and many others are contained within the circle. Someone you can’t see is playing the aforementioned upbeat (almost eerily so, now that you can see the whole picture) tune on the bagpipes, and nearly everyone is dancing—but not in a choreographed manner you might see from a flash mob today. Instead, this dancing is convulsive and jerky, and almost out of control—like there is a maniacal puppet master manipulating their movements from above.

As you cautiously take a few steps closer to this bizarre scene, you see that many of the dancers are staring blankly up at the sky, as if in a trance. Occasionally, they yell—shriek might be the more appropriate word—unintelligibly into the air. Some of these shrieks become agonized screams, and you can clearly make out the word “help!” shouted at least once or twice. You notice that, in the middle of the circle, several couples are on the ground having sex with one another. The whole thing looks like a drug-fueled ritual/orgy, but it’s taking place right out in the open, for everyone to see.

One of the dancers suddenly falls to the ground and starts convulsing. He’s clearly having some sort of seizure, his body thrashing about wildly and uncontrollably—but everyone just ignores him. After what must be about 30 seconds, he recovers, slowly gets up, and begins dancing again.

Think of the shock and horror you would feel when you encountered this scene. Now consider that if you lived in certain parts of Europe between the fourteenth and seventeenth centuries, this spectacle may not even have been cause for alarm. These types of dancing displays were not unheard of, and it’s very possible you would have seen one before.

In those days, the people who participated in the dancing rituals were thought to be afflicted by some malady (often assumed to be demonic possession) that led to compulsive dancing. The ailment was deemed contagious, and it was believed onlookers could be overcome and compelled to join the dancing at any moment. The condition was often called the dancing mania or St. Vitus’ dance, the latter name coming into use because the afflicted would often dance near the churches or shrines of St. Vitus, the patron saint of dancers. Priests from these churches frequently tried to intercede, frantically attempting to exorcise the demons from those who were affected before they were able to pass the sickness on to members of the clergy.

A depiction of dancing mania by Pieter Brueghel the Younger.

One such event occurred in 1374 and spread across a large area of Europe that included western Germany, Belgium, the Netherlands, Luxembourg, and northeastern France. Dozens of independent chroniclers of the events agree that thousands of people were affected, and the dancing went on for weeks. Another incident in Strasbourg in 1518 involved around 400 people, a number of whom were reported to have died while dancing in oppressively high summer temperatures. There were many other smaller occurrences of dancing mania, and sporadic reports of it persisted up until the mid-1600s.

While it’s possible some of the details of these events have been embellished, the number of independent verifications of them suggest they did occur in some form. So what could have caused this strange behavior? To this day, scientists are stumped. Some have suggested the culprit might have been widespread ergot poisoning. Ergot is a fungus that grows on rye; it has strong psychoactive effects when it’s ingested, and it can cause hallucinations, tremors, and convulsions (a constituent of ergot, lysergic acid, can be used to synthesize LSD). Is it possible, then, that widespread consumption of tainted rye could have led to these “epidemics?”

It doesn’t seem very likely. Ergot poisoning is characterized by spasms and convulsions, but also by symptoms like nausea and diarrhea, making it improbable sufferers could have danced for days on end. Additionally, ergot poisoning often involves the appearance of gangrene (i.e. tissue dying due to a lack of blood flow—it causes gruesome blackened skin that’s difficult to overlook) on the toes and fingers, but reports of dancing manias don’t include such descriptions. Finally, outbreaks of dancing mania also sometimes occurred in regions where rye wasn’t a common crop.

Of course it’s possible there was some other environmental exposure we haven’t identified that had a widespread influence on behavior, but such things are difficult to ascertain so long after-the-fact. And due to the lack of viable alternative explanations, many scientists have begun to believe the dancing mania was a manifestation of something called mass psychogenic illness, or MPI.

MPI involves the appearance of symptoms that spread throughout a population, but don’t have a clear physical origin. In other words, in MPI the brain is causing the patient to think they are afflicted by some ailment—even though the brain itself is the creator and orchestrator of the illness. This doesn’t mean that the symptoms aren’t real; there can be legitimate physical manifestations of MPI. But there’s no evidence the symptoms are produced by something (like a poison or a germ) other than the nervous system.

MPI is surprisingly common throughout history. Before dancing mania, there was a condition known as tarantism that occurred during the Middle Ages in Southern Italy. Victims of tarantism suffered from a number of symptoms ranging from headache to difficulty breathing, which, according to the victims, began immediately after the bite of a tarantula. (In those days, tarantula referred to a wolf spider, not the spiders we typically think of as tarantulas. Regardless, whether a spider bite was really involved was usually difficult to verify; it’s suspected that in many cases, the spider—like the resultant condition—was a phantom of the mind.) Once the malady took hold, however, the victims didn’t seek out antidotes to spider venom. Instead, they immediately began to take part in the only recognized cure: dancing. Patients would dance on and off for hours, days, or even weeks to upbeat melodies now known as tarantellas (this is what you heard in the video clip above).

Since these dancing disorders of the Middle Ages and early modern times, there have been hundreds of other potential instances of MPI as well. But, you might be thinking, perhaps MPI occurred in the distant past because people were more superstitious and easily-duped than they are today. Surely, we must have advanced past this era of gullibility, right?

Wrong. There is a long list of examples of possible MPI in modern times. For instance, in 2011, twenty classmates at a high school outside Buffalo, NY suddenly began to experience tics, verbal outbursts, and other symptoms that resembled those of Tourette syndrome. Despite investigations by doctors and state health department officials, no environmental cause of the condition was identified, and most doctors eventually agreed that the students’ conditions were brought on by psychological factors. Some doctors even suggested that social and mainstream media contributed to the “spread” of the affliction. Those who were more inclined to post frequently about their ailment on sites like Facebook and those that gave frequent interviews to the press were thought to have the most aggravated conditions. The students who avoided these practices tended to improve more quickly.

Havana syndrome is potentially an even more recent example. Havana syndrome began in late 2016 in Cuba, when American and Canadian diplomatic personnel started reporting a number of symptoms—like headaches, nausea, dizziness, memory problems, hearing loss, and even “mild brain trauma”— which typically appeared after hearing a prolonged harsh, high-pitched noise. Strangely, other people nearby usually didn’t report hearing anything. By 2018, up to 40 cases of Havana syndrome had been documented among American and Canadian diplomatic personnel in Cuba. And in early 2018, similar claims began to be made by U.S. diplomats in China.

At first, many thought this was a case of international espionage at its finest—perhaps Moscow testing a secret acoustical weapon. But evidence to support that theory is lacking, and a number of scientists have now decided it’s more likely the diplomats were experiencing MPI. (Some have even suggested the high-pitched noise the diplomats heard was actually the sound of a particularly noisy type of cricket.)

There are many more examples of MPI in both modern times and the distant past. So, what is actually going on here? Well, first it’s important to point out that it’s almost impossible to completely eliminate other potential causes in these cases. There’s always the chance the unexplained symptoms linked to occurrences of putative MPI could be better explained by a toxin in the environment, a pathogen, or something else altogether that we just haven’t been able to identify. Perhaps, for example, Havana syndrome really was caused by some new weapon being surreptitiously tested by the Russians. We don’t know for sure.

But it’s also likely that at least some of these cases of potential MPI are due mainly to psychological factors. And if so, we’re at a loss to explain how, exactly, that might occur.

Some have suggested that extreme stress, pushing the brain to its cognitive breaking-point, might be a risk factor. Dancing mania, for instance, often affected areas that had recently been ravaged by harsh societal blights like food shortages, devastating diseases, etc. Others have argued that MPI preys primarily on the most suggestible people in the population. According to this hypothesis, there are some who are simply more inclined to believe a mysterious illness is taking hold of them, especially after they’ve heard about or seen someone else affected by that “illness.” (These might also be the same people who are most likely to be susceptible to the influence of something like hypnosis.) And still others are unconvinced that MPI is a viable diagnosis in many cases, since it implies a certainty we can’t possess (that there is no other cause of the condition) and assumes we have the ability to explain behavior that might have been prompted by any number of factors ranging from actual physical illness to cultural elements we may not completely understand.

Thus, at this point, MPI is controversial. We can’t explain why it might happen, and we also can’t say for sure how often it really does. But, there are many scientists who believe this type of mass hysteria is a legitimate phenomenon that has the potential to affect anyone, given the right circumstances. That’s a sobering thought, although it’s still unclear if it’s grounded in reality or if it, like the condition in question, is merely an example of the inherent fallibility of the brain.

References (in addition to linked text above):

Bartholomew RE. Tarantism, dancing mania and demonopathy: the anthro-political aspects of 'mass psychogenic illness'. Psychol Med. 1994 May;24(2):281-306.

Waller J. A forgotten plague: making sense of dancing mania. Lancet. 2009 Feb 21;373(9664):624-5.