It may seem obvious why teens engage in risky behavior, but what you may not know is that scientists have found that some teenagers are especially hard-wired to making bad decisions about sex, drugs, and alcohol.

Atika Khurana, an assistant professor of counseling psychology at the University of Oregon, led a study published in the journal Child Development that found that differences in the brain’s working memory could explain why some adolescents are especially impulsive, according to an NPR report.

Working memory allows the brain to remember other things — such as, perhaps, consequences — when making a decision or solving a problem.

In the study, Khurana and her colleagues looked at 360 adolescents between the ages of 12 and 15 and used a series of test to assess their working memory. They would read off a list of random numbers to the kids and have them repeat it in reverse order.

The research team than tracked those participants for two years and inquired about their sexual activity, putting them through more tests and surveys to gauge just how impulsive each teen was.

They found a correlation between weaker working memory and the likelihood of a teen having sex at a younger age. They also seemed more likely to act without thinking, even when other factors were taken into account.

Working memory is in development throughout adolescent years, but it can happen at a different rate, which means some teens may be more vulnerable to making poor decision at that age than others, even if they eventually develop the necessary working memory. It’s why sex education doesn’t always work.