What we know about fear and the brain

August 6, 2018

A friend came home to this recent surprise: a copperhead enjoying the late-day sun on her front stoop. She grabbed a hoe and chopped it into little copperhead parts. She was moved to silently apologize for violating nature’s creation. But after all, her fear-related mechanism had kicked in. That story pops out of my memory bank, creepily, every time I wander in my quasi-woodsy backyard.

To be human is to be fearful—one aspect of a conscious engagement with the world. To be human is also to be curious, including curiosity about fear.

Duke’s Kevin LaBar and Ahmad Hariri, professors of psychology and neuroscience, are well-positioned to address that curiosity. Visiting with them in the fearsomely hulking Levine Science Research Center, I found them remarkably cheerful in talking about fear. They see fear as a necessary emotion and a necessary experience, since, of course, experience instructs us. The challenge is for us to control our fear responses so that they’re adaptive—so that they help award us meaningful, rather than limited, lives.

Fear may be everywhere, but it manifests in a wide spectrum of human behavior. Anxiety, the two experts explained, is closely related to fear. But anxiety can be thought of as a more general apprehension about some possible future event. And anxiety disorders are more generalized. So I’m anxious, though perhaps not fearful, on the occasion of International Asteroid Day, when there’s a lot of speculation about the ultimate high-impact scenario. As for snakes: They’re simply fear-inspiring.

Hariri talked about individuals driven by “high reward,” even in the face of threats—seeking, say, the thrill of jumping off a diving platform. My favorite mini-doc, Ten-Meter Tower, plays with that theme; the Sweden-based documentary tracks people as they confront a ten-meter, or thirty-three-foot, diving board. All of them hesitate, observing the obvious—“It’s a long way down!” But they also respond to social pressure (and to the pressure of the camera), as people on the pool deck shout, “You’ll be so happy afterward!” About 70 percent of the would-be divers made the jump. The non-jumpers showed a threat-mitigating mindset: the thought of landing with a painful splash, or worse.

Extremes in the fear-response spectrum can be debilitating. But as a society, Hariri told me, we’re helped by individual differences. We want the person who says, Let’s hurl ourselves over to the next valley, don’t you think it could have nicer streams and fields? And we want the person who says, Hold on, what if another clan has claim to that next valley, and what if they have more rocks and spears than we do? There you have the risk-taker and the risk-avoider, each with a different way of processing potential threats.

LaBar and Hariri are interested in a particular aspect of the brain, the amygdala, that’s all about processing potential threats. It’s best to think of it, they said, not so much as a discrete structure but rather as a circuit, or a collection of neurons and their connections, that supports associative learning. That is, it helps train the brain to recognize a threat and to fire up the appropriate action.

The amygdala does all of that first by capturing direct input from the senses. It might process a faint but ominous growling sound from nearby bushes and tell the body that it’s time to release a bunch of stress hormones. Those stress hormones signal, essentially, “danger ahead, take evasive action.” They actually do more than wave the warning flag. They might direct blood flow to muscles used for running, and to decision-making centers of the brain.

Still, you want the amygdala to defer to the higher authority and moderating influence of the prefrontal cortex— guiding you against tossing tiny pebbles at the menacingly growling creature, an action that might end your individual evolutionary line. As Hariri put it, this “primitive, instinctive system” isn’t right for every circumstance.

The amygdala helps update your memory bank, so that in the future, you know enough to avoid walking by the same creature-containing bushes. But depositing specific fears in the memory bank has a downside, which LaBar has explored with MRI scanners. He’s fitted research subjects with stereoscopic goggles and presented three-dimensional virtual worlds—basically immersive movies—into which snakes or spiders, or more innocuous objects, might be inserted. One key finding: As humans, we have very context-sensitive fear responses. What happens when that subject “revisits” the same virtual environment—maybe a wooded scene that earlier featured a virtual snake—later on? Even if the onetime threat is absent, the memory is embedded.

The fear memory may be embedded, but over time, it can be overridden. That offers hope, said LaBar, for treating post-traumatic stress disorder; there, the fear-inspiring episode is ever-present. Imagine you have a fear of snakes. The memory of a snaky run-in is tied up with a particular context or environment. Your fear has become generalized to woodsy walking trails. Then imagine going through a series of simulations in virtual reality. You’re exposed and re-exposed to a woodsy walking trail. And nothing bad happens. Nothing snaky.

That fear-based aversion may not have gone away completely. But it’s diminished to the point that you’re no longer associating the great outdoors with a gruesome encounter.

All of which doesn’t erase the fact that there are triggers in our evolutionary history. Hariri referred me to a study in which six-month-old infants, shown pictures of snakes and spiders, consistently reacted with larger pupils—a sign of focused attention. They reacted more moderately to images of flowers and fish. But it’s a complicated picture, he told me. With those agitated infants, we might not be seeing full-fledged fear responses. Rather, we might be seeing a fear-based predisposition to certain stimuli, a response that crystallizes over time and with direct or vicarious experiences.

Back when we lived in small clans, Hariri said, some of those threat-tinged experiences might have been with someone unfamiliar. Now, living as we do in a large human society with intricate, complex networks of individuals, fear of the stranger is not a healthy driver of our behavior. However unhealthy, fear of “the Other” is an easy avenue for demagoguery: We tend to see a potential threat in the “out group” that somehow is not like us. A lot of research, LaBar told me, shows that the range of fear responses includes clinging to a group identity. That identity might be expressed by race, language, or nationhood—indicators of the “in group.”

Our many global interconnections, then, may be playing on our fears. At this point in our evolutionary history, there are fear incubators in our patterns of living, including our speedy communications, our forms of transport, and even our dense urban environments. Employing the local version of the Star Trek holodeck, the Duke Immersive Virtual Environment, or DiVE, LaBar and his team have programmed avatars to approach research participants at the same distance as an airplane seat: first in an upright position; then in a reclining position. As the encounter gets closer, the perceived threat becomes scarily imminent, and the “startle reflexes,” as LaBar calls them, kick in: a scrunched-up face, muscle tension, increased blood ow, sweat glands going into overdrive.

His particular interest there is the so-called “recliner rage” that afflicts us in-flight. More broadly, he’s measuring a direct and immediate threat suggested by violations of personal space. Snakes on a plane are scary, as classic cinema tells us. So are tightly packed people on a plane.

With that overview of some experiments, LaBar and Hariri left me with a lesson: We know a lot about fear and the brain. We also know that the world—not just its supply of snakes and spiders—is increasingly fear-inspiring.