What causes risky behavior? 12,000 brains may reveal the answer

Pre-Covid, the ultimate social faux pas was to show up late, again, to your BFF's birthday drinks (now, of course, the faux pas is to show up at all). A common excuse: The traffic is abysmal. If you've been there, you know how tempting it is to just hit the gas when a green traffic light turns to amber.

Do you speed up, hoping to make it through the light safely? Or do you hit the brakes and wait for the red light to play out? According to a recent study, what you actually decide to do in these little, everyday moments may be more telling about how your brain is structured than you think.

Assuming you're not in a self-driving car, there are a number of factors that will play into these split-second decisions, but all of them add up to one question — is it worth the risk?

What's new — Gideon Nave, an associate professor of marketing at the University of Pennsylvania, is co-author of the study, published January 28 in the journal Nature Human Behavior. Nave and his team were interested in defining how a person's genetics affect her capacity to take risks.

Nave tells Inverse that genetics does play a role, but there is still much more to learn.

“If I look at a group of people, I can, on average, predict [a tendency to take risks],” Nave says. “I know something about you.”

But based on one person's brain, it is hard to make such predictions, Nave says. Rather, these changes become apparent at the group level, but one person's brain is ultimately unique to them. So to get around that limitation, Nave and his team went big on the brains: In total, they looked at the structure of 12,000 brains for this study.

To explore this idea, let's stick with the traffic scenario. How late you are, how fast you’re going, and even the strength of your friendship are taken into consideration as you drive. But there’s also something more fundamental at play, too: your biological capacity for risk.

How they did it — Nave and his team used the UK Biobank, a massive dataset including brain scan and genetic data from more than 12,000 people aged 40 through 69 years. In the sutdy design, they controlled for a wide variety of factors which could play into risk taking — from age and gender, to excessive alcohol consumption.

The control for alcohol matters. The reason, Nave explains, is the brains of people who consume excessive alcohol tend to look different to people who don't have alcohol abuse issues.

“Alcoholics definitely have a brain that has lower grey matter volume all over the place,” Nave says.

“But with a very large sample, you can also find effects in moderate drinkers.”

In the study, "part of the risky behavior we look at is related to drink," Nave says.

Back to the hypothetical driver late to a birthday party. If they drank before they got in the car, their decision-making process would be altered.

“You want to make sure that the effect is not driven” by a third margarita, Nave adds.

Why it matters — The human capacity for risks isn't limited to speeding up for yellow lights, or even drunk driving. Humans take risk into account every day, and in any number of areas — from gambling, to attending parties, to potentially catching Covid-19 at a bar.

Understanding why we make these decisions can ultimately help researchers and physicians better mitigate adverse kinds of risk-taking behaviors, like a gambling addiction, or drug abuse problem.

The big idea — The human brain is complex, with a wide variety of clusters and regions that make up how we process thought. So it makes sense that there isn’t one direct relationship between the brain and risky behavior.

"We find that we don’t have only one brain region that is the ‘risk area,’” Nave says in a press statement. “There are a lot of regions involved.”

There are so many genes related to the risk-taking process that Nave and his co-authors decided to use a measurement of genetic variation, called a polygenic risk score.

Polygenic risk scores essentially put a value on how a person's risk for something, like a disease, behavior, or other trait compares to someone else with a different genetic make up.

“There are traits where the samples are becoming larger and louder, when we start to be able to predict quite well,” he says. This is true, for example, of traits like educational attainment, Nave says. Some studies, Nave says, can predict “about 15 percent of the variance between people from their genome alone.”

For risk-taking behavior, the team found polygenic risk score could explain about 3 percent of the variation in risky behavior. This may seem small, but when they drilled down further, the team discovered an interesting correlation between polygenic risk score and the amount of grey matter in the brain. Grey matter refers to the cortex of the brain.

The scientists focused in on three regions of the brain. In so doing, they found 2.2 percent of genetic disposition toward risky behavior may be predicted by the volume of grey matter each region contained.

In a statement accompanying the research, Philipp Koellinger, a professor of genoeconomics from Vrej University Amsterdam and co-author on the study, said the “grey matter of these three regions is translating a genetic tendency into actual behavior.”

For Nave, a further surprise came in the form of the brain scan data.

Nave found risk-taking people showed cranial regions that were anatomically distinct to their peers — something which has been shown before. To see the same result is a “very nice convergence that I was not expecting to this degree,” he says.

For example, the researchers discovered the amygdala, a region associated with taking risks, appears to be altered in the brains of people with high polygenic risk scores for such behavior.

“It turns that people with small amygdalas tend to take more risks. That’s reassuring to see in a very large sample,” he says.

What’s next — As is often the case with the brain, every new neuroscience study leads to yet more unanswered questions. In this case, the data suggest a curious and relatively unexplored connection between the cerebellum and risky behavior. Historically thought of as being strictly related to motor control, Nave says “several cerebellar regions seem to be related to risk taking.”

He speculates these difference may be related to drinking behavior, however, which may alter the structure of the cerebellum. But with the scientific evidence growing for a connection between the cerebellum and decision making, its possible scientists have “been missing something,” Nave says.

Start to solve one brain puzzle, and another might just spring up in your path.

Abstract: Previous research points to the heritability of risk-taking behaviour. However, evidence on how genetic dispositions are translated into risky behaviour is scarce. Here, we report a genetically informed neuroimaging study of real-world risky behaviour across the domains of drinking, smoking, driving and sexual behaviour in a European sample from the UK Biobank (N = 12,675). We find negative associations between risky behaviour and grey-matter volume in distinct brain regions, including amygdala, ventral striatum, hypothalamus and dorsolateral prefrontal cortex (dlPFC). These effects are replicated in an independent sample recruited from the same population (N = 13,004). Polygenic risk scores for risky behaviour, derived from a genome-wide association study in an independent sample (N = 297,025), are inversely associated with grey-matter volume in dlPFC, putamen and hypothalamus. This relation mediates roughly 2.2% of the association between genes and behaviour. Our results highlight distinct heritable neuroanatomical features as manifestations of the genetic propensity for risk taking.