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How Havana syndrome helps us rethink the brain

A neurologist explains how its weird symptoms can manifest via a common but misunderstood class of brain ailments.

People on the steps of a building titled Embassy of the United States of America, seen through an open wrought iron gate.
Workers at the US Embassy in Havana leave the building on September 29, 2017.
Emily Michot/Miami Herald/Tribune News Service via Getty Images

Ever since 2017, US officials, medical doctors, and psychological researchers have been mystified by a string of “sonic attacks’’ that have been reported around the world. Dubbed Havana syndrome after several US personnel at the American embassy in Havana, Cuba, complained of a range of symptoms including headaches, fatigue, dizziness, hearing loss, and nausea, the condition has attracted enduring debate over what could cause it.

Last week, a group of US intelligence agencies released a report that all but crossed one high-profile possibility off the list. The report concluded that it is “very unlikely” that Havana syndrome was caused by a foreign adversary.

But the US intelligence agencies don’t think people who suffered through this condition were just making it up. “These findings do not call into question the very real experiences and symptoms that our colleagues and their family members have reported,” the office of the director of national intelligence wrote in a press statement.

So if it wasn’t caused by a weapon from a foreign adversary, and the personnel weren’t making it up, what was it?

Some have claimed this is an example of mass psychogenic illness — i.e. outbursts of strange group behavior like “dancing mania.” But this may not be the most helpful way of thinking about it, according to Jon Stone, a neurology professor at the University of Edinburgh in Scotland.

“When patients hear the word psychogenic, they think that’s a doctor accusing me of imagining my symptoms,” says Stone. Instead, he says, there’s another plausible, arguably overlooked explanation here: a functional neurological disorder, or FND.

An FND is essentially a disorder of brain functioning, but not one caused by an obvious physical problem, like a stroke. It’s more about how the brain communicates with itself.

FNDs can be kicked off by something like a fall, a virus, or an episode of vertigo, but then, rather than improving, the brain gets stuck in an extended state of dizziness, nausea, or fogginess. That initial cause can also be stress or anxiety. In diagnosing someone with an FND, neurologists have to make sure the patient isn’t suffering from an underlying medical condition like multiple sclerosis or a stroke.

Stone says he often explains FNDs to patients as being like software errors on a computer. “If a program crashes on your computer ... would you assume you would find a burnt-out circuit that explained to you why your computer was not working? You wouldn’t,” he says. “There’s something going wrong with the software.”

FNDs are easily misconstrued, and, according to Stone, are understudied as well. But they’re actually quite common. “They are probably the second-commonest reason for an outpatient visit to a neurologist,” says Stone, who runs a clinic for functional disorders. And while it’s not always possible to see an FND on a brain scan, it’s possible to see structural changes from FNDs on brain imagery across large groups.

On a 2021 episode of the Unexplainable podcast, I spoke with Stone. He explained that the growing understanding of FNDs breaks down the tidy categories we like to draw around concepts like psychology and neurology. An FND is certainly not the only explanation for patients with Havana syndrome, but it shows just how powerful and complicated the brain can be.

Below is an excerpt of our conversation, edited for length and clarity. There’s much more in the full podcast, so find Unexplainable on Apple Podcasts, Spotify, Stitcher, or wherever you listen.

Noam Hassenfeld

Do you think the idea of an FND can help explain the reports of Havana syndrome?

Jon Stone

I think it should just be on the table, and it should be on the table without prejudice and without assumptions that people seem to be making about it.

Noam Hassenfeld

So if we take the idea of a weapon from a foreign power out of the equation, why would people be experiencing these symptoms? What’s a possible FND that could explain it?

Jon Stone

I don’t know whether there may be an external phenomenon [like a weapon], but ... we see quite commonly, for example, in neurological practice a disorder called PPPD, which stands for persistent postural perceptual dizziness. This is where people have typically had an episode of vertigo from a more easily defined cause. And then instead of recovering in the way that most people do, their brains get stuck as if the acute vertigo is still happening and they feel dizzy all the time.

When anyone gets vertigo or acute dizziness, they normally adapt to it. They lie in bed and they sort of tense their body when they’re moving, and then as the vertigo improves they recover to health. But some people maintain those abnormal physiological adaptations and they continue to feel dizzy for weeks, months, and years.

Typically, the symptoms will get worse over time as these Havana syndrome patients’ did, because the patients got stuck with an abnormal program in their brain that is saying, “There is dizziness. You must do this in response to dizziness.” This is not a program that the patient can reach into their own brain and change. They are feeling dizzy. You can’t suddenly switch that off. But it’s a disorder that you can’t see on a scan.

Noam Hassenfeld

Why would this just be happening to this small targeted community of foreign diplomats?

Jon Stone

Well, it might be that there is something causing dizziness. But ... if you take a few thousand people and you ask them about day-to-day physical symptoms like fatigue, concentration, dizziness, those symptoms are incredibly common. Most people feel tired, for example, some of the time. Most people feel a bit dizzy some of the time.

We just did a study of healthy 20-year-olds in Edinburgh and showed that about 20 percent were having symptoms that if they presented to a neurologist, you might say, do you have cognitive problems? Because they’re doing things like forgetting where they park their car or putting their keys in the fridge. But because they’re 20-year-olds, they’re not interpreting those as a problem. They’re just saying, “Oh, well, I just forgot what my car was.” So physical symptoms are present at quite a high rate in the population.

If there is a particular trigger or someone suggesting you have to look very closely for these symptoms, it’s possible to get an even higher frequency of symptoms. I think it is possible that a lot of anxiety may be caused [by] the possibility of having a brain injury from a sonic attack. And that that concern is heightening people’s vigilance for events that might be consistent with a sonic attack. And then subsequent symptoms that might be consistent with a sonic attack. That does not mean that if they’re suffering from that, they have brought it on themself or that they’re imagining it.

I think when you’re looking at the data, what’s very hard to work out is what is the denominator here? How often would you expect diplomats to get episodes of vertigo due to migraine? Due to other other causes? There are many reasons why people feel dizzy.

Noam Hassenfeld

But some of the symptoms I’ve heard seem a lot more serious than just a migraine. People say that they’ve felt different for years. They didn’t just have episodes of dizziness, they had persistent dizziness, persistent fatigue, persistent nausea. They had to leave their jobs.

Jon Stone

Yeah, so I don’t know if [Havana syndrome] is a functional disorder, but if you came to my clinic in Edinburgh, you would watch me interview lots of people who’ve been nowhere near an embassy, who have persistent dizziness and cognitive problems, fatigue, which means they have to leave their jobs. And which gets worse year on year. So to me when I read about these patients, I’m reading about patients who are just people I would see every time I do a clinic. And yes, perhaps there was a sonic attack causing this syndrome. But these are not unusual illnesses. These are common illnesses, one of the commonest types of illness seen in a neurology clinic.

Noam Hassenfeld

If some of this may have happened because people are hearing about brain injuries and becoming more attuned to their own symptoms — maybe attributing commonly occurring dizziness to something external — would the patients have needed to be in contact with each other to start worrying? It’s been reported that some of the patients didn’t know each other and hadn’t seen each other.

Jon Stone

Well, I would say that all of the patients that I meet with the same disorders haven’t met each other either. And they have the same symptoms. People have had these symptoms from different types of functional disorders all over the world. I talk to neurologists in Tanzania and rural Pakistan, it’s the same symptoms, often with different interpretations, but the same symptoms and experience.

Noam Hassenfeld

So how would we categorize FNDs, then? Are they psychological?

Jon Stone

Historically, neurologists have approached these symptoms as psychosomatic or somehow arising from the mind. But in the last 10 or 20 years, a sort of flowering of research in this area has helped to understand these disorders as ones that are at the interface between neurology and psychiatry, where it is reasonable to talk about them as clinical brain disorders.

And there are examples of that that everyone’s quite happy with [not referring to as just psychological]. So for example, phantom limb syndrome, a soldier has their leg amputated. But they still have the experience of their leg being there because the map of their leg in their brain is still there. And they experience very distressing phantoms of the limb being there. It’s painful. Is that a psychological problem? You wouldn’t necessarily say so. You would say, “Well, that’s a kind of brain problem.”

Noam Hassenfeld

That’s the exact thing that I’m struggling with here. Can you help me define this concretely? What is the difference between psychological and neurological?

Jon Stone

Well, what I’m saying is that we shouldn’t have those boxes, and this is why you’re struggling. Because you’re trying to think about disorder with a framework which is dualistic, in which you only have these two boxes. Neurological and psychological refer to the same organ. And it can go wrong because of structural change, it can go wrong because it’s not functioning properly. And this is why it’s so hard, I think, to report these things or help people get their head around, because we have dualistic language. I’m a neurologist. It’s in my job title. We have psychiatrists. Everything is telling us that there are these two categories, when I think neuroscience is telling us that there aren’t.

Noam Hassenfeld

A lot of the patients who have experienced these symptoms have gotten upset when they’ve heard people claim that Havana syndrome wasn’t caused by an attack, that it could have been psychogenic or an FND. Do you feel like there is a misunderstanding of what an FND is?

Jon Stone

Yeah, there’s a massive amount of stigma and misunderstanding. And this area, still, it’s really very poorly taught, if taught at all at medical school, even though as soon as doctors graduate, they realize that quite a large proportion of their patients have these problems. So we are dealing with a difficult area where people very commonly bring their prejudices to it, their prejudice that if something is psychosomatic, then it’s not real. So I do understand why when patients hear the word psychogenic, they think that’s a doctor accusing me of imagining my symptoms or being crazy or making them up. I personally don’t use the word psychogenic because it suggests that the problem is all psychological.

For me, these disorders [are] actually forcing us to have a whole new way of thinking about what is the brain, what is the mind. People who come to my clinic really can’t move their legs, they really are dizzy all the time, they really can’t think straight, and they are suffering from these conditions. So for me, someone with dizziness or cognitive problems or movement problems from FND is just as genuine as someone with MS or stroke. But I realize that from a societal view, people just don’t have that box in their head. The only boxes they have are you’ve got some sort of brain damage or brain disease or it’s not really a thing and you’re just kind of imagining it.

Noam Hassenfeld

There was a team at the University of Pennsylvania who took MRIs of some these patients, and they say they found results that are consistent with a major brain injury. Would those results eliminate the possibility of an FND?

Jon Stone

Here we get into more of a pickle because it turns out that even disorders like FND, depression, anxiety, if you look very closely at large groups, you actually do start to see changes in structure as well, because the brain is in some ways a bit like a muscle and it will grow in some bits and shrink in others. People with post-traumatic stress disorder have shrinkage of certain parts of their brain. So brain imaging is really, I’m afraid, no way to make arguments that things are neurological or psychological. And that’s why we have to abandon those categories.

And it becomes very harmful to [patients] if they’re caught in a legal system or in the medical system that’s telling them this is all brain damage. Because essentially what that means is this is the way you’re going to be forever. There’s no possibility of improvement. Your brain is damaged. Now, it’s very validating for the patient. But if they do have a functional disorder, it’s potentially very harmful because you’re denying them the opportunity to consider treatment of their condition through other means.

Noam Hassenfeld

So if someone with Havana syndrome came to you, and you did diagnose them as having an FND, what would your treatment be?

Jon Stone

So if I see a patient who’s got the type of symptoms described in Havana syndrome and they fulfill diagnostic criteria for a functional disorder, the treatment involves beginning with explanation. If you’re trying to sort out a problem where the patient’s own brain is going wrong, you have to help them understand what’s happening. To make sense of it as a starting point. That there’s a software problem in the brain that we want to try and retrain the brain. Now you can retrain the brain through physical therapy. So if someone has a weak leg or a movement disorder or to some extent dizziness, then physical therapy can be helpful, and we’ve learned that those therapies need to be focused on FND as a treatment.

And psychological therapy can also be helpful in retraining the brain, changing patterns of thinking or expectation, the ways that people respond to symptoms when they arise. How do you respond to a particular incident where your memory really let you down? Do you think, “Oh my God, that’s my brain damage again?” Or do you think, “Okay, well, actually, 20 percent of the population have that experience from time to time, is it as bad as I think?” So broadly speaking, it’s physical and psychological rehabilitation that we use to try and help improve these disorders.

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