Ever get the feeling you're talking to a brick wall when trying to communicate with your teens? Well, a new study suggests there may be some science to it, after finding that teenagers' brains start tuning out their mothers' voices around the age of 13. Researchers said that this is because they no longer find it “uniquely rewarding,” and instead tune into unfamiliar voices more.

The study by the Stanford School of Medicine used MRI brain scans to give the first detailed neurobiological explanation for how teenagers begin to separate from their parents. It suggests that when your teenagers don't seem to hear you, it's not simply that they don't want to clean their room or finish their homework—their brains aren't registering your voice the way they did in pre-teenage years.

Lead study author Daniel Abrams said, “Just as an infant knows to tune into her mother's voice, an adolescent knows to tune into novel voices. As a teen, you don't know you're doing this. You're just being you: You've got your friends and new companions and you want to spend time with them. Your mind is increasingly sensitive to and attracted to these unfamiliar voices.”

Researchers said, “The brain's shift toward new voices is an aspect of healthy maturation. A child becomes independent at some point, and that has to be precipitated by an underlying biological signal. This signal helps teens engage with the world and form connections which allow them to be socially adept outside their families.”

A study published in 2016 showed that children can identify their mother's voice with extremely high accuracy. Even fetuses in utero can recognize their mother's voice before they're born. Yet with adolescents their brains are tuning away from their mother’s voice in favor of voices they've never even heard.

Brain responses to voices increased with teenagers' age. In fact, the relationship was so strong researchers could use the information in adolescents' brain scans to predict how old they were. When teens appear to be rebelling by not listening to their parents, it is because they are wired to pay more attention to voices outside their home.