National Geographic : 2013 Jun
34 national geographic • june 2013 exhilaration that continues after the threat has passed, as the adrenaline clears the system. For some people that adrenaline rush can become a reward the brain seeks. They are prompted to induce it by going to scary movies or engaging in extreme sports or by artificial means such as taking narcotics. But adrenaline isn’t what motivates explorers to take risks. “An Arctic explorer who’s slog- ging through ice for a month isn’t motivated by adrenaline coursing through his veins,” says Zald. “It’s the dopamine firing in his brain.” Critical to this process is how the brain measures risk. Photographer Paul Nicklen de- scribes how his definition of acceptable risks has evolved over time. “When I was a kid living in the Arctic, I would paddle ice floes like rafts, which was probably risky. Then I learned to dive, and I just kept wanting to go deeper, stay in the water longer, get closer to the animals. “For a long time I told myself I wouldn’t dive with Atlantic walruses,” he says. “The reason there aren’t many photos of Atlantic walruses swimming under polar ice is because it’s in- credibly difficult and dangerous to cut a hole in ice that’s several feet thick and dive into water barely above freezing and try to get close to 3,000-pound animals that can be highly ag- gressive when disturbed. There are a lot of ways to die doing that.” Nicklen’s reward for taking those risks is capturing walrus images that are so close, so three-dimensional, that they cast a spell over a reader. “I want readers to feel like they are a walrus, swimming with other walruses. For fleeting moments, that’s what I feel like at times. The only way I can describe how powerful a feeling that is is through these pictures. I guess I am sort of addicted to it.” The movement of Nicklen’s personal “risk line” is his brain’s way of recalibrating risks based on past experience, says Larry Zweifel. “He is very comfortable recognizing what po- tential threatening situations look like and how to successfully avoid those situations. His brain calculates the risks and the potential reward, facilitated by his dopamine system, which then motivates him to do the dive.” And yet, says Zweifel, “if he were to repeat- edly dive with animals that threaten his life and encounter many near-death experiences but continue to make such dives regardless of the negative outcomes, then that would be compulsive behavior, which can become pathological, like losing everything because of a gambling problem.” Acclimating to risk is something we all do in our daily lives. A good example of this oc- curs when learning to drive a car. At first a new driver may fear traveling on freeways, but over time that same driver with more experi- ence will merge casually into speeding traffic with little consideration for the significant potential dangers. “When activities become routine and famil- iar, we let our guard down, especially when nothing bad happens for quite some time,” says Daniel Kruger, an evolutionary psychologist at the University of Michigan. “We have a sys- tem designed to react to short-term threats, but when it is on all the time, it can have a detrimental impact on the body,” such as el- evating blood sugar and suppressing the im- mune system. This familiarity principle can also be applied to help deal with the fear associated with high- Senior writer Peter Gwin wrote about Africa’s rhino-poaching epidemic in the March 2012 issue.