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Welcome to the Betterment Lectures. My name is Dr. Dorian Minors, and if there’s one thing I’ve learnt as a brain scientist, it’s that there’s no instruction manual for this device in our head. But there are patterns—patterns of thought, of feeling, of action. That’s what brains do: create patterns that gracefully handle the predictable shapes of everyday life.
So let me teach you about them. One pattern, one podcast, and you see if it works for you.
Today I want to talk about something that really occupied me during the COVID lockdowns in 2020. Stuck in my little apartment studying brain science, I was struck by some of the more bizarre ways people were responding to already fairly extreme circumstances. You had lockdowns. I, as an Australian in the UK, couldn’t make my way back to Australia—they weren’t really letting us back into the country, the lockdowns were so stringent. And the response globally was, to some extent, alarming. The response to the vaccine was often alarming. The responses to the initial fears around the virus itself were alarming.
It reminded me of a concept you learn in undergrad psychology: shared madness, or folie à deux, the madness of two. They use it as a bit of a hook, because it’s not really how we think about it anymore. The idea is that two otherwise normal people somehow go insane. One person suffers some delusion or hallucination, and the other ends up sucked into it too, and together they do quite crazy things.
What struck me in the pandemic was how some of the features of that seemed to have an uncomfortable similarity to what we were seeing in people during the lockdowns. And when I was exploring the idea—both back then and when I dug the articles up and republished them—I came to this uncomfortable conclusion. I don’t think shared madness is necessarily rare. In fact, I think we’re all kind of vulnerable to the circumstances that lead people to catch it.
So let’s talk about it.
I want to start with a pretty famous example: a couple of Swedish women travelling from Ireland into the UK. This happened maybe 20 years ago now, but it’s still something people in the UK talk about today.
These women were on a coach—coming in towards Liverpool, I think—and they were behaving so oddly that the driver decided to leave without them after a service-station stop. They were acting suspiciously, oddly fixated on their bags. The driver later said he was worried for the other passengers, and the service-station manager seems to have agreed, because they were worried enough to call the police. The police turn up, ask some questions, and decide there’s nothing wrong with these two women—who then proceed to wander down the motorway, occasionally sprinting across it, insensible to the rushing traffic.
Of course, the police are called again. And as they’re talking to the women for the second time, next to the motorway, with no apparent trigger, one of them sprints into the oncoming traffic and gets hit—followed shortly after by the other, who sprints in after her sister and gets hit too. Both are badly hurt.
At this point, being loaded into ambulances, they’re recorded saying some quite strange stuff. Things like “I know you’re not real”, and one of them shouts that “they’re going to steal your organs”. Fairly bizarre. They end up in hospital, and one recovers fast enough to be released that afternoon. The other is held a little longer, because her injuries are more severe.
The released sister goes out onto the street and starts wandering, ostensibly trying to locate her sister, and is eventually taken in by a kind couple who were themselves out walking. She goes back to their house, has dinner, stays the night, and stays the entire next day. She was generally pretty friendly, but still acting strangely—going to look out the window, saying the cigarettes they were smoking might be poisoned. Strange enough that one of them wondered if she was running from an abusive partner. Anyway, the second day, after staying the first night, they’re sitting down to dinner and she stabs one of them to death, runs out into the night, and is spotted not long after on CCTV beating herself in the head with a hammer she’d picked up along the way.
Very, very strange behaviour from start to finish, over several days. And the interesting part is there were no drugs involved—toxicology turned up nothing. No history of mental illness in the family, no criminal convictions. Just two ordinary women, two ordinary sisters, one of whom left a family behind on her abrupt visit to Liverpool. Three or four days of madness that ended in substantial tragedy.
This is the classic case of folie à deux: people with no particular history of illness come together and engage in really bizarre behaviour. And it’s a pretty well-studied phenomenon. The modern history dates back to the 1860s or so, when a French neurologist called it folie communiquée—communicated madness. He described a couple so tangled in each other’s delusions that the doctors couldn’t figure out who had gone mad first. About a decade later, a couple of French doctors gave it the name that stuck, folie à deux, which is what people still use in the clinical literature today.
But it extends past the madness of two. There’s an entire taxonomy. You have folie imposée—imposed madness, where one person’s delusions are imposed on the other—as opposed to folie simultanée, where both people are already a bit delusional and the two sets come together and settle on some middle ground. And then folie à trois, the madness of three; folie à famille, the madness of a family. Today we just call it shared psychotic disorder.
The criteria are pretty strict. You need a delusion shared among the people. You need intimacy. And you need each person—whether it’s two of them or a whole family—accepting, or at least supporting, the others’ delusion.
I tell you all of this not just for background, but to make it clear that it seems like a very rare, quite bounded
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clinical curiosity. We don’t hear about cases like the two Swedish sisters sprinting into cars very often. So you might imagine this never happens—and that whenever it does, it’s not likely to happen to you.
That’s the idea I want to subvert a little today. So let me see if I can convince you otherwise.
One thing that should give us a clue that this isn’t a nicely bounded clinical phenomenon is the growth of the taxonomy itself—from the madness of two, to the madness of three, to imposed versus communicated, to the madness of a family. Even as it was being documented for the first time, it immediately started to balloon outwards.
The reason is that the spectacular cases—the sisters on the highway, the violence and bizarreness that characterise the cases we see in the media—aren’t really the important factor. What’s core is intimacy in the context of social isolation. That’s the original qualification for the disorder, and it’s the feature you see repeated again and again: lonely people, isolated together, and in that context an intense intimacy forms. That’s the fertile soil that lets a delusion take such hold over people’s behaviour. The delusion itself is almost incidental.
Once you concentrate on intimacy in the context of social isolation, my interest in this during the COVID lockdowns makes a bit more sense. But it also makes you wonder how rare it really is—because not all delusions are violent enough to make the news.
And that does seem to be the case. The academic literature itself admits that shared madness is under-diagnosed—clinicians have trouble spotting it, because often only one half of the pair turns up for treatment. I’ll put some links in the show notes, but to quote one:
Patients with shared psychotic disorder can go undiagnosed because only the primary partner is registered for treatment in a classic presentation … Awareness of the nature of the dyad relationship dynamics is necessary.
The reason we don’t always catch the dyad comes down to how we think about abnormal psychology. I go into this in more detail elsewhere, but essentially: you need a reason to ask people to come in and have their problem solved. We don’t just assume weirdness is something clinical to be fixed. For us to treat it, that weirdness has to meet one or more of a few criteria. It might be statistically rare. It might be culturally rare. Most importantly, these days we concentrate on the distress model—does it cause the person, or the people around them, distress? And a final model is risk of harm, to yourself or others.
But a delusion doesn’t have to violate any of these. If you’re under the impression that people who don’t exist live in your house, but you think them quite benign, why would you go to the doctor? So we often find, in cases of shared madness, that one person suffers the delusion—and it might lead them to behave more strangely—while another doesn’t really suffer it but simply accepts it, and as a consequence it doesn’t drive their behaviour strongly enough to rise to our attention.
There are mundane cases that enter the literature but that you never hear about in the news. One common example is shared pseudocyesis—a phantom or fake pregnancy—which is actually not that uncommon in couples who’ve been struggling with infertility, and which can sometimes produce real physical pregnancy symptoms. Another is delusional parasitosis, a shared, unshakeable belief that some kind of infestation is being passed between people. It appears quite often in the academic literature but rarely makes the news, even when the cases are quite strange.
The most interesting one I discovered, looking up cases for this article, is a Japanese family of four who all came to share the youngest son’s hallucination. The son believed—and I’ll quote the article—that:
a jelly-like substance or amoeboid materials come out from my mouth, and people around me react to those materials.
First the son believed this, then his mother, then his twin brother, and finally the father—all of them, in the end, seeing this jelly-like material and reporting that they observed other people affected by it. An entire family. Not a headline anywhere. So not quite so isolated as someone paying attention to the news might be led to believe—because the news cares more about the cases that end in tragedy or violence, that aren’t just strange but really consequential.
These cases made it into the literature. But remember that clinicians don’t always catch people. I suggested that might be because some people are more driven by the delusion than others. But a lot of people caught up in episodes of shared madness don’t believe the delusion at all. They just can’t leave, for one reason or another.
A case in Australia a few years back: the Tromp family fled their farm and drove hundreds of kilometres in terror of some following threat—unspecified, but frightening. Some members ended up, just from the reports, in quite substantially altered states; others seemed more confused than anything else. Afterwards, everybody was as baffled as the people trying to work out what they’d been running from. To quote a couple of them—first:
It’s very confusing. I still feel confused.
And a second:
You do start thinking in the same way. You can get sick in some kind of way.
One member of the family, Mitchell, was explicit that he never shared the fear at all. He just, in his words, couldn’t leave them behind. So even within a single case of shared madness there’s a difference between the people who believe the delusion, the people who accept it, and the people who don’t believe or accept it but are simply staying for some other reason.
So I hope I’m starting to paint the picture. You start with a clinical disorder that, on the surface, sounds quite tightly scoped. But the taxonomy’s own development shows you it quickly ballooned—from a madness of two to a madness of three, imposed versus communicated, to the madness of a family like the Tromps
in Australia. Then you look at the gap between the news presentations, which concentrate on tragedy and violence and fear, and the clinical presentations, which never make the news even though they’re quite weird. And then the clinicians themselves tell you they have trouble identifying cases, because not everyone presents abnormally enough to be treated. And, all that aside, not everyone is engaged in the delusion the same way—from the people who believe it, to the people who simply accept it, to the people who stay, not because they believe or accept it, but because they can’t leave.
Once you’ve got a phenomenon with edges this fuzzy, you start to wonder whether cases we characterise as something else might actually be shared madness. The example I use in the article that inspired this lecture is Theranos—the famous failed-unicorn Silicon Valley company. Elizabeth Holmes raised more than $700 million from venture capital and private investors, at a valuation of around $9 billion if I remember correctly, to develop blood tests that could be performed rapidly and accurately with tiny amounts of blood, using these nifty little automated devices the company had supposedly developed. As it turned out, a couple of years later, all the claims were false—and it became a famous example of not just fraud but Silicon Valley hubris: investing in companies blindly, not worrying too much about what you’re investing in.
But there’s another reading of what happened. Holmes and her partner at the time, Sunny Balwani, shared what was well known to be an intensely intimate and enmeshed relationship—so much so that one of Holmes’s defences was that it was a case of abuse and coercion. What’s interesting to me is that, in an environment like this, you don’t just have the headline case—the fraud, the blind investment. You also have a sort of strangeness. A dog that Holmes pretended was a wolf was permitted to roam the sterile halls of the company, defecating and urinating wherever it liked. There are reports of Holmes speaking in different voices. And whether those are substantiated or not, there was rampant paranoia within the organisation itself.
One wonders whether this is exactly the kind of isolation-plus-intense-intimacy required to produce shared madness—perhaps between Holmes and Balwani, but also among a horde of people around them who didn’t necessarily need to believe the delusions at the core, but had to stay because they couldn’t easily leave. Add some textbook group polarisation, or risky shift—the well-known phenomenon where groups push themselves further than individuals would alone—and you have what could be a case of shared madness, filed away as Silicon Valley hype. It doesn’t read that way to us, because “tech elites being weird” is already a frame that explains it well. And that’s my point: if there’s a tidier pattern than shared madness available, we might never reach for the explanation of shared delusion. We miss it by having a better story.
Let me conclude with a few more examples that could be something like this, and some implications, before I let you go.
Shared madness is, I should be clear, a clinical case of disordered human behaviour. My point is that, given the conditions that sit at its core, and how hard it is to characterise it at its fuzzy edges, a lot more human behaviour might be attributable to that very dynamic than to whatever frame is more convenient for us. And if that’s so, it might mean we’re more vulnerable to it than we make out.
Take internet phenomena like gang-stalking, where people believe they’re being followed by individuals on the street in a coordinated way. Or Morgellons, where people report that they, or the people around them, are suffering from strange fibrous parasitic wounds. Or many of the reported cases of mass psychogenic illness—dancing fevers and the like. Often, particularly with the advent of the internet, these cases involve exactly the kinds of social isolation and intense relationship dynamics characteristic of shared madness. And very infrequently are those factors considered, because the cases fit other patterns a bit more neatly.
The common thread is intimacy plus social isolation. And social isolation isn’t a rare misfortune—it’s one of the single biggest threats to human health we face in the modern world, both mental and physical. If loneliness is endemic, and we can generate intense closeness not with the people we live with but with people online, then you’ve got the soil for this—both in ordinary kitchens and in group chats and Discord servers.
When we’re starved of connection and we finally find a home in someone else, we’ll go to extraordinary lengths to keep it. That’s not a pathology. That’s just us, working as designed. All it takes is for somebody to start having strange beliefs, and under those circumstances we could all be vulnerable to shared madness—in a modern world where we’re able to get information faster than ever before, communicate more easily than ever before, but are equally more isolated than ever before.
I wonder just how much of the craziness we see is really an extension of shared madness: intimacy in the context of social isolation.
I’ll leave it there.