Ever wondered why you got more careful with age? It's certainly not what you thought.

Older folks tend not to engage as much in risky behavior as teenagers and young adults do. You might call that wisdom or learned experience. But this also may be a result of lower amounts of gray matter in the brain, according to a new study.

Researchers at Yale and New York University found that adults in the study who were less inclined to take risks had less gray matter in a brain region called the right posterior parietal cortex, which ― you guessed it! ― is involved in decisions that entail risk.

In the study, the researchers asked adult volunteers ranging in age from 18 to 88  to play a game involving risk. The volunteers were allowed to choose between a guaranteed gain, such as pocketing $5, or an uncertain gain, such as a lottery to earn between $5 and $120 with varying chances of winning ― or losing.

As the researchers expected, those participants who chose the guaranteed gain — that is, no risk — tended to be older than those who opted for the lottery. It wasn't a perfect correlation, but it was close. One could call this old-age wisdom. [7 Ways the Mind and Body Change With Age]

Yet when the researchers analyzed brain scans of these volunteers obtained through an MRI technique called voxel-based morphometry (VBM), they found that lower levels of gray matter, even more than age, best accounted for their risk aversion. 

These results suggest that the changes in the brain that occur in healthy aging people may be behind more of our decision-making patterns and preferences than previously thought, the researchers noted in their findings, published today (Dec. 13) in the journal Nature Communications.

The relationship among decreased risk-taking, declining gray matter and aging makes sense from an evolutionary viewpoint, said Ifat Levy, an associate professor of comparative medicine and of neuroscience at Yale University, senior author on the study. 

"In many ways, it makes sense for older adults to take less risks than younger ones, both because they may be less able to stand the consequences, and because they have less time to live and 'fix' the damage," Levy told Live Science.  "Another way to think about it is that, for older adults, it may be enough to have just a little bit — of food, money, etc. — to keep them going, so they don't need to take the chance.  Younger adults need to take care of offspring and so on, and the 'safe' option may simply not be enough to achieve everything they need."

Levy said that she would like to extend the brain research to adolescents. In a previous study, Levy and her colleagues demonstrated that teenagers have a tolerance for ambiguity, which can increase their participation in risky behavior when the risk is unknown. 

Michael Grubb, first author on the current study — who at the time of conducting it was a postdoc at NYU and is now an assistant professor at Trinity College in Hartford, Connecticut — said the research team had only just begun to scan the brains of adolescents, and it was not yet clear how levels of gray matter affect their affinity for risk.

"The picture is complex," Levy said, with factors such as peer pressure and a brain not yet fully developed acting as contributing factors.

Or, for teenagers, it may be that the answer is gray.
Credit:livescience