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It’s the fifth inning and the Tampa Bay Rays are beating the Cleveland Indians 6–2 when Cleveland’s relief pitcher Nick Hagadone steps in. Alas, Hagadone does little to turn around the Indians’ luck that day, closing out the long inning with a score of 10–2. Hagadone, apparently frustrated by his own lackluster performance, heads to the clubhouse and, on the way there, punches a door with his left fist — the fist that is, unfortunately, connected to his pitching arm.

That momentary impulse would cost him dearly. Hagadone required surgery and eight months’ recovery time — and, to add insult to a literal injury, his team also relegated him to the minor leagues, a move that shrank his annual salary by more than 80 percent. When asked about what could possibly explain an action like this in a usually easy-going guy, the Indians’ team psychologist, Charlie Maher, could only offer variations on this: “He just snapped.”

Unless you are also a relief pitcher in the major leagues, you will likely never be in exactly this situation. But how many times have you reacted aggressively, even violently, in a way that felt almost out of your control? You hurl your smartphone across the room, or you unleash a stream of expletives in a manner that would seem to a calmer, rational mind to be disproportionate to the situation at hand. “I just snapped” is how we explain it to ourselves and others, and then we move on. The phrase has become such a cliché that it’s easy to forget that it doesn’t really explain much of anything. What’s behind this impulsive, immediately regrettable behavior?

R. Douglas Fields, a senior investigator at the National Institutes of Health, sought out an explanation in his new book, Why We Snap: Understanding the Rage Circuit in Your Brain, which includes the Hagadone story recounted above. “I wanted to know what it means from a neuroscience level,” Fields told Science of Us. “I think that the word is kind of in common usage, and we understand it maybe from a psychology perspective — that is, it’s a break with reality — but I wanted to know what‘s going on inside the brain.”

Fields argues that there are nine major triggers that invoke the rage response, which he has assembled into the acronym LIFEMORTS: life and limb, as in your physical safety; and insult, meaning a verbal threat. The next six are self-explanatory: family, environment, mate, order in society, resources, tribe — you already know each of these are things you’d fight for if you felt they were in danger. The last is stopped, the idea that any animal (humans included) will ready itself to fight if it feels restrained or trapped. So for each of these nine triggers, the rage kicks in to prepare you for a potential fight, because you feel like something essential has been threatened.

These triggers evolved in our brains for a reason, and at times they give rise to defensive action that is as necessary for modern humans as it was for our early ancestors. But they can misfire, too, sometimes to violent, irreversible effect. Fields spoke with Science of Us about what happens inside the brain when we flip our proverbial lids, and how we can begin to control this impulse.

So a thing that sparks the most inexplicable rage in my small life is my incredibly, frustratingly slow internet connection at home. Which trigger could that be?

That’s a good example. It’s the S trigger, and the S stands for stopped. You’re stopped — it’s like you’re being restrained. And any time an animal is restrained, it will engage in an aggressive reaction to get free. It’ll chew its arm off if it’s in a trap. And people will do the same thing — you know, that backpacker who cut his arm off when he was trapped. And that’s extreme violence.

But here’s the key: Your internet’s slow, or you’re stuck in traffic. Why are you suddenly angry, fuming angry, instead of some other human emotion, like dreadfully bored? That is because anger is [meant] to prepare you to fight. That’s what it’s there for. It’s tripped this trigger to prepare you to fight, because you are trapped. And the minute you recognize that — you’re on the internet and nothing’s loading, and you start to get riled up — if you just think, Oh, I’m angry because of the S trigger, it just goes away. You realize kicking at your screen is not going to solve this problem.

Let’s back up. What does “snapping” mean, exactly, anyway?

We read in the newspapers every day things like, “He was a perfectly good, quiet, peaceful person, and he just snapped.” And then the story just moves on. Well, that doesn’t explain anything! What does that mean?

The way I defined it, it means that this sudden act was inappropriate and that the person did it without any conscious thought and, immediately afterward, almost always regrets it. So those are really peculiar things.

And when you look at the news stories, you see that the majority of violence and murder and the things like this that fill the pages are not being done by mentally ill people. They’re regular people, in domestic disputes or barroom brawls, who suddenly have this impulsive, angry response.

Can you walk me through what you found — what is happening inside the brain when a person “snaps”?

Again, there are two key features here: It’s not conscious, and it happens rapidly. So this is part of the brain’s threat-detection response mechanism. When we’re confronted with a common threat, we have the neural circuitry to respond quickly and aggressively to that threat. That neural circuitry is all subcortical; it’s not conscious. If you dodge a basketball, it comes flying into your peripheral vision, and you react. This is actually a really complex motor reaction, where you will duck, raise your hand, close your eyes — all of that happens before you’re aware of it.

So what’s happening here is that an enormous portion of the brain is devoted to threat detection — that system runs from the prefrontal cortex to the amygdala to the hypothalamus, all the way across the brain. And this threat-detection mechanism is constantly taking in information from all of our senses, every one of them — and internal senses, too — constantly assessing the situation in our internal and external environment for threats. So this information streams into that subcortical part of the brain before it ever goes to our conscious brain.

And the minute something is received as dangerous, or threatening, it invokes this defensive physical reaction. That’s the connection between snapping and threat detection, and that explains why we’re bewildered after we react in this way. Because just in the same way that you will dodge a basketball before you even consciously know it’s coming, or jump out of the way of a car that narrowly misses you in a parking lot — it’s the same kind of feeling when you, you know, start using purple language because somebody cuts in front of you on the highway. It’s that same feeling. Both of those situations have tripped defensive circuits in the brain.

Right, because there are clearly times when we unconsciously react in ways that are positive, right?

The key to snapping is, we wouldn’t have these circuits if we didn’t need them. When they work, we call it quick-thinking. Many times it’s called heroism — think about the young men on the train who stopped the terrorist attack in Paris this summer. So somebody will jump in and risk their life for somebody else, and immediately afterward they say, “Well, I didn’t think — I don’t know why I did that.” It’s the same thing.

And we see this in sports, where somebody makes just a spectacular play. It’s identical circuitry in the brain; we only call it “snapping” when it’s tripped this aggressive response inappropriately. So that’s the problem. We have all this circuitry in our brain, because human beings evolved in the wild in a survival-of-the-fittest environment. And our brain we have today is the same one we had 100,000 years ago. But our environment is totally transformed. So what happens is you have situations in the modern world that didn’t exist — like driving a car — causing these defensive circuits to misfire.

Because, you know, most of the time this works amazingly well. Only occasionally it misfires. And that’s what we want to control.

And you argue in your book that if we understand which trigger has been set off, we can defuse some of that unnecessary rage.

I do. And that’s why I came up with the LIFEMORTS mnemonic, so you could quickly identify, “What is the reason for this sudden rise in anger?”

So, say somebody just runs a stop sign. When somebody does this and you see it, you’re just instantly consumed with anger. And that’s really interesting, if you think about it. Why anger? Why not some other emotion? And if you can see that it’s one of these defensive circuits — in this case, it’s the O trigger, for order in society — you will instantly know two things: One, you’re in a situation that is about to release a potentially violent reaction, because it’s hardwired in the brain to do something like that in response to these threats. And, two, if you recognize that this anger is caused by something in the modern world setting off this circuitry in a situation where getting in a physical fight is not going to be helpful, you instantly disarm the whole circuitry.

But what’s the difference between this and anger-management techniques?

Well, anger management is good, and lowering stress is good — all those techniques are good. But we all know if somebody’s angry, and you tell them to calm down, it doesn’t help. It actually makes people more angry.

By identifying the trigger, on the other hand, it turns this whole situation into kind of a game. So I’ll give you an example. I was in the airport with my daughter, and we were all jockeying to get on the plane — you know, how you board by your group number and everything. And somebody cuts in front of us. And my daughter just starts laughing. And she goes, “Oh, it’s the O trigger,” and then we both start laughing. Normally, a person cuts in front of you, and the hair stands up on your back, and you feel enraged and angry. And in many cases in that situation people get into arguments, and they snap. I see this now, and it helps me on the road a lot — somebody cuts in front of me and I think, Oh, that’s the E trigger. I’m concerned about protecting my environment. And to me, it’s like the anger just goes away, because I realize this is completely inappropriate. Suddenly you realize, Oh, this is not worth a fight, and the feeling goes away.

But if there’s a real situation, you know, god forbid, a deadly situation or a dangerous situation, somebody invades your house, that same E trigger that misfires so often in driving will be tripped. And so to protect your environment at home, if you have to, you will engage in violence to do it. So it won’t inhibit it if the urge to fight is appropriate.

You know, as we’ve been talking I started thinking of a group that often becomes irrationally angry: little kids! Would this work with an angry kid, or a teenager, for that matter?

Yes, I think so. What kids and teenagers need to know is, “Why are they angry?” You can’t just tell them, “Don’t do that, that’s not right.” They already know that. The problem with a kid and a teenager is they do not have the circuitry developed — their prefrontal cortex isn’t developed yet — so to tell them to call on a part of their brain that doesn’t exist is not going to work. My real hope is that this could be taught to kids at school, so they could suddenly understand, It’s not that I’m a psychopath — it’s that it’s tripped this trigger of rage in a situation that’s completely inappropriate. They don’t need to suppress the anger; it’s that they need to understand why they’re angry. And it’s one of those things that just defuses it.

You know what it is? Just understanding something is the first step to being able to control it and use it. If everyone could understand, look, we have these defensive circuits in the brain — they’re important; they’re helpful 99 percent of the time; they work amazingly well. But sometimes, in our modern world, they misfire. That’s so much different, and more useful, than saying, “Don’t get angry,” or “This guy’s crazy.”