Last week, the world was captivated by the dramatic search and rescue operation in the North Atlantic for a missing submersible carrying five people. Four of those aboard were tourists looking to explore the wreckage of the HMS Titanic at depths of over 12,000 feet. Tragically, the submersible imploded before the search and rescue mission even began. All aboard would have died instantly.

All on board knew death was a real possibility, mentioned several times on the waivers they all signed. Why do intelligent people choose to engage in risky behavior, whether it be in the ocean depths, rock climbing, or base jumping? Some call it brave; others call it reckless. Emory University psychology professor Dr. Ken Carter joined All Things Considered host Arun Rath to break down the psychology of so-called “adrenaline junkies.” What follows is a lightly edited transcript.

Arun Rath: The term “junkies” implies addiction. Using the term in a clinical sense, can a person actually be addicted to adrenaline?

Ken Carter: It’s interesting because adrenaline may not necessarily be the thing that they’re seeking. We talk and think about them as “adrenaline junkies,” but really, what they are are sensation seekers. They’re seeking unusual sensations of the mind, of the senses, of physical sensations as well, and they’re doing that despite the risks that may come with that.

Rath: Obviously, not everybody is built this way, but do we have a sense of the kind of people who are likely to become what we might call adrenaline junkies?

Carter: We know we’re all sensation seekers of some sort, but the high-sensation seekers—and there’s a researcher, Marvin Zuckerman, who started research on this—are seeking those sensations despite the risks. And there are some interesting psychological and physiological features that they may not necessarily be perceiving those things as risky as those who are average- or even low-sensation seekers.

Rath: Talk a bit more about that. That’s fascinating that we’re not all seeing things the same way.

Carter: So, one of the chemicals that are in our body that gets us ready, you know, that fight or flight or freeze response, is called cortisol. It sort of organizes our body systems to help us fight a perceived threat. So, low-sensation seekers, like me, have lots of cortisol whenever those things are around us that might create some danger or even curiosity. So our bodies will perceive those things as dangerous.

High-sensation seekers can be in really chaotic environments, but they’re not sending off the same chemical alarms, so they don’t really excrete as much cortisol, so their bodies don’t perceive those things as stressful. But at the same time, they have another chemical that we all have called dopamine, which is associated with pleasure. During those highly chaotic experiences, they excrete more dopamine and less cortisol. So, those really dangerous seeming things for the rest of us seem more exciting and less scary to them.

Rath: I’ve read about how, in certain animal groups like crows, for instance, there’s a certain tendency for certain individuals to be more aggressive and risk-taking, and there’s a kind of evolutionary biological reason for that. Can we say that there might be something similar going on here?

Carter: There are lots of advantages to having some people in our society as sensation seekers. You know, these are people who work in emergency medicine, first responders, you'll see them out helping with the rescue. And so, when they're in those highly chaotic environments, they can focus, be organized and get stuff done.

You know, even though I'm a low-sensation seeker, you don't want someone like me around during those kinds of emergencies because that cortisol is going to cause us to flee or freeze, and you need people who can work through that.

Rath: Are there any elements of simple personal psychology to this? You know, one has to have a lot of confidence to engage in these kinds of behaviors. How much is internal versus external?

Carter: So, there are a couple of pieces to that. Number one, they're not perceiving it as dangerous, and so they may not be thinking that they're being confident. But from an outsider's perspective, like for me, what they are doing is they sort of trust their bodies in a way, and they're going to throw themselves into some experiences and be convinced they're going to figure it out along the way. And most of the time, they do. You want people like that in emergencies who are not going to overthink things but are going to put themselves in those situations.

But you're right; there are some environmental pieces to it as well, including the kinds of things that we choose to do if we're high-sensation seekers. Not everyone has the money to heli-ski or do adventure-type sports. So instead, what they'll do is drive fast or not back down from arguments. And so, the kinds of choices we make in terms of the things that we do for sensation seeking are absolutely impacted by our environment.

Rath: Is there a line at which this kind of thrill-seeking behavior becomes unhealthy and becomes a problem for the individual?

Carter: So, there are two components to the personality that can help us predict that. There are four different pieces to the sensation-seeking personality, and two of the ones that sort of help us to predict how much trouble a person might get themselves into is how much inhibition they have towards their sensation seeking and how easily they get bored.

Not all high-sensation seekers get bored easily, and many of them plan out their activities very carefully. You know, we've seen people climb up Mount Everest or go into outer space or be able to rescue people from burning buildings. We don't think about them as being dangerous people. But for a small percentage of them, it can get them into trouble.