Vaughan Bell is a clinical and research psychologist based at the Institute of Psychiatry, King’s College London. He’s also working on a book about hallucinations due to be out in 2013.
Cheerleaders from a small town in New York state have been making headlines because several of them began to display tics and involuntary movements that have been diagnosed as conversion disorder---a situation which has often described in the media as being due to "mass hysteria" or a "mystery illness." I can't say for sure whether the diagnosis of conversion disorder is accurate or not because I've not been clinically involved with the affected people, and if I had, I couldn't talk about it due to patient confidentiality, but what I can say is that some of the media reporting of conversion disorder, "hysteria" and its related concepts has been highly confused. Hysteria is used in everyday language to mean "panic" but it has a long history as a medical condition, originating from Hippocrates who thought that a whole range of symptoms could be caused by the womb "wandering" around the body. As you might expect, it was traditionally thought of as a female disease until the French neurologist Jean-Martin Charcot shocked the medical world by reporting the first male cases. Although the connection with a wandering womb was comprehensively disproved, doctors were still puzzled by patients who seemed to have neurological disorders without damage to the brain and nervous system. The core definition of hysteria as neurological symptoms without neurological damage remains with us today. A student of Charcot's, Sigmund Freud, became curious about the condition and added another element to the definition, which both made his career and became the basis of psychoanalysis itself. As a neurologist, Freud came to believe that mental energy was equivalent to neural energy and, therefore, our mind obeys something akin to the laws of thermodynamics. The first such law says that energy cannot be created or destroyed, only converted into another form. This is why Freudian psychology is full of mechanical concepts such as "repression" and "conversion" and the idea that all emotional disturbance must be "processed" or "dealt with" (think: a release valve) or else it will express itself in another form (think: a burst or bulging pipe). Many of the theory's predictions have been disproved but the theory lives on and, to a great extent, it has become what we unfortunately think of as common sense. Nevertheless, Freud applied the same thinking to hysteria, saying that these seemingly neurological symptoms can appear without neurological damage because the unconscious mind is shutting down the body to prevent us from encountering a deep emotional disturbance. A bit like locking the basement in a rushed attempt to deal with a burst pipe---the problem is easier to ignore but not any less serious. As Freud fell out of fashion, many people assumed that the concept of hysteria had gone with him, but this is not the case. Although his theory about hysteria being caused by the "unconscious repression of trauma" isn't very popular among scientists, it's a simple fact that patients can develop what seem like neurological disorders---such as paralysis, blindness, seizures, and tics---despite having a perfectly functioning nervous system. And despite popular claims that the condition is rare or "doesn't happen any more," it still commonly presents in neurological clinics. Numerous studies have found that up toone-third of patients who consult with neurologists typically have symptoms that are not fully explained by neurological damage. So how can these "pseudo-neurological symptoms" be distinguished from genuine neurological disorders? Neurologists can rule out such damage to the nervous system because they are specialists in the lower-level machinery of the brain---the neurology rather than psychology. As an analogy, while you may not understand how your iPhone works, an electronic engineer could check every component and electrical connection to try to pin down the source of a problem. If each part were working fine, we would know that an issue that would normally be caused by physical damage, such as a loss of sound, was actually due to a software problem. In this situation, neurologists do something similar for the brain. If the patient can't hear, a neurologist tests the electrical parts of the hearing system; if those work, then it must be an issue with how the functional hearing circuits are being coordinated by the control systems. In brain terms, this doesn't mean there isn't an issue, just that it's not due to low-level nervous system damage. This is also why it is unlikely that the New York teenagers' problems are linked to an "unknown virus", "mystery illness," or "toxin," which many media outlets mentioned as potential causes: Viruses, bacteria, or poisons are most likely to cause these symptoms by damaging the neural pathways---something we can normally detect fairly easily. Cynics might suggest that conversion disorder patients are just faking, but we have good evidence that this is not the case. The majority gain nothing from their disability, making a poor case for deception. What's more, neuroimaging studies show that someone with conversion disorder paralysis has markedly different brain activity during an attempt to move an immobilised limb, compared to people who have been taught to fake the same symptoms. So when the LeRoy cheerleaders were diagnosed with "conversion disorder," the doctor was saying that although the symptoms appear to be due to neural damage, there were no problems with the neural pathways, and there was no evidence of faking, so the symptoms were likely due to psychological factors. "Mass hysteria," on the other hand, is not a recognised diagnosis and just describes where seemingly physical symptoms with no medical explanation affect a whole group of people at once---usually with the suggestion that a temporary conversion disorder-like syndrome is the cause. As the history of mass hysteria shows, the effects can be astounding at times. But even with a diagnosis like conversion disorder, there remains the question of how the brain is causing these strange effects. Talk of "psychological factors" just shifts the burden of explanation from the brain circuits that directly deal with movement or sensory functions to those involving "higher" brain functions that coordinate and control them. What studies are increasingly showing is that these symptoms might be generated by the involuntary control, or tamping down, of brain areas that control sensory and movement functions. In this case, the systems doing the involuntary control are thought to be the higher-level brain functions like attention and executive function that rely heavily on the frontal lobes. Our own research group recently reviewed brain-imaging studies of people with conversion disorder and found that when patients try and do something contrary to their impairment---for example, trying to move a limb paralysed with conversion disorder---activity in the frontal lobes massively increases, as if the control mechanisms were suddenly putting the brakes on. Nevertheless, we're still not entirely sure why this situation occurs in the first place---why does the brain's control system decide to hit the brakes, destabilize a coordination system, or cause unnecessary movement? We have some clues. It turns out very similar brain activation patterns occur in hypnotized people if they are given suggestions to simulate conversion disorder-like symptoms, but these effects are temporary, unlike conversion disorder, which can be long-lasting. We know that patients with conversion disorder are more likely to have other forms of emotionalinstability. While the Freudian idea of conversion disorder as a direct unconscious attempt to repress or avoid painful thoughts is unlikely to be accurate, it may be that unstable emotion might be adversely affecting the control of more basic sensory and coordination systems in the brain, and this may help us explain why some patients have conversion disorder in its chronic form. The effects of "mass hysteria," however, typically pass quickly, perhaps suggesting that social suggestion might be a more important cause for these sorts of temporary outbreaks. It's worth noting that despite its long history we still know relatively little about hysteria, partly because it falls thought the cracks of medicine, as it is usually detected by neurologists but is best treated by psychologists or psychiatrists. However, anyone who has seen its effects knows that the old cliche about the power of mind over body has a ring of truth to it.