We all love rewards, but they often come packaged with risks. The most mundane decisions we make every day can involve such trade-offs. Should you hit snooze on the alarm for an extra few minutes of slumber, and risk being late, or drag yourself out of bed? Should you eat the delicious leftovers in the fridge from last week, risking a possible stomachache or worse? Sometimes the risk-reward trade-off requires a bit more thought: Should you take up sky diving in your 40s, just for the hell of it?
The study of how we calculate risk versus reward is called decision neuroscience, and it got its start almost 30 years ago. Over the past several decades, neuroscientists have reported that losses loom larger than gains, that the human brain hates ambiguity more than risk, and that we tend to value immediate rewards more than future ones. Scientists who study how we make decisions have also determined that to calculate a choice’s value, we rely on a network of many different areas and systems in the brain, including its risk and aversion centers, the amygdala and insula, and the dopamine system, which tracks whether a risky bet paid off. We also rely on the anterior cingulate cortex, which calculates effort and cost, and the orbitofrontal cortex, which sits at the very front of the brain just above the eye sockets and plays a role in emotion and reward processing.
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Now a team of scientists has identified a precise area in the orbitofrontal cortex where risk-reward decisions are calculated. The scientists—from University of California, San Francisco, and University of California, Berkeley—were also able to predict the actual choice a person would make a half second before they did at a rate better than chance. And they found that the way these risky decisions take shape is less like a dial, where accumulating evidence reaches some threshold, and more like a see-saw, with two patches of the brain signaling in opposite directions as a person swings between approach and avoidance. The findings were published today in Nature Neuroscience.
Study author Clara Starkweather, a neurosurgery chief resident at UCSF, designed an immersive video game for the experiment. The objective of the game, which you can play yourself, is to rack up the maximum score in rubies. To gather your rubies, you must navigate a maze of hallways lined with different numbers of lit bombs and treasure chests containing the red gemstones. “There’s just one decision point—whether you go down each hallway,” said Starkweather in a release.
Study subjects included six epilepsy and psychiatric patients undergoing brain monitoring for surgical treatment with electrodes already placed directly in their orbitofrontal cortex. The scientists monitored these electrodes for activity while the patients played. Eerie music emerges as you navigate the dungeon-like hallways, and you can hear your own footsteps and heavy breathing as you approach the bombs and treasure. Each lit bomb that explodes costs you a point. But sometimes, the lit bombs don’t go off and the chests are full of rubies, and you are rewarded for the risks you took. If you don’t like the risk-reward trade-off offered by a particular hallway, you can navigate to the next one.
Starkweather and her colleagues found that when the gamers were making an easy decision—a hallway full of treasure and zero explosives—the “go” cue got the upper hand very quickly. When the decision was harder, with treasure and bombs in equal measure—participants teetered between “go” and “avoid” cues, like a see-saw, before swinging in a final direction. The researchers could often predict how a patient was going to act just before they did based on how this brain activity played out.
Risk-taking and risk-avoidance behavior play an important part in a number of psychiatric conditions. People with depression, anxiety, and obsessive compulsive disorder often are overly risk-averse, while people with gambling and addiction disorders tend to take too many risks, with unfortunate consequences. Risk-taking tends to peak in adolescence, something that some developmental neuroscientists attribute to a faster rate of maturity in reward circuitry than control circuitry.
“Right now, psychiatry mostly relies on asking people how they feel,” Starkweather said. “I want to give it something more objective: a real, measurable signature of how someone’s brain weighs risk, so treatment can target the specific circuit that’s off.” 
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