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.

Around age 13, kids’ brains no longer find their moms’ voices uniquely rewarding, and they tune into unfamiliar voices more, a new study from the Stanford School of Medicine has found.

The research, which was published April 28 in the Journal of Neuroscience, used functional MRI brain scans to give the first detailed neurobiological explanation for how teens begin to separate from their parents.

“Just as an infant knows to tune into her mother’s voice, an adolescent knows to tune into novel voices,” said lead study author Daniel Abrams, PhD, clinical associate professor of psychiatry and behavioral sciences. “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.”

(Abrams explains how children's attention to voices evolves in this video.)

In some ways, teens’ brains are more receptive to all voices — including their mothers’ — than the brains of children under 12, the researchers discovered, a finding that lines up with teenagers’ increased interest in many types of social signals.

However, in teenage brains, the reward circuits and the brain centers that prioritize important stimuli are more activated by unfamiliar voices than by those of their mothers. The brain’s shift toward new voices is an aspect of healthy maturation, the researchers said.

“A child becomes independent at some point, and that has to be precipitated by an underlying biological signal,” said the study’s senior author, Vinod Menon, PhD, the Rachael L. and Walter F. Nichols, MD, Professor and a professor of psychiatry and behavioral sciences. “That’s what we’ve uncovered: This is a signal that helps teens engage with the world and form connections which allow them to be socially adept outside their families.”

Age-related shift toward new voices

The Stanford team previously found that, in the brains of children 12 and under, hearing Mom’s voice triggers an explosion of unique responses: A study published in 2016 showed that kids can identify their moms’ voices with extremely high accuracy and that the special sound of Mom cues not just the brain’s auditory-processing areas, but also many areas not triggered by unfamiliar voices, including reward centers, emotion-processing regions, visual processing centers and brain networks that decide which incoming information is salient.

“The mother’s voice is the sound source that teaches young kids all about the social-emotional world and language development,” said Percy Mistry, PhD, co-lead author and a research scholar in psychiatry and behavioral sciences. “Fetuses in utero can recognize their mother’s voice before they’re born, yet with adolescents — even though they’ve spent even more time with this sound source than babies have — their brains are tuning away from it in favor of voices they’ve never even heard.”

The new study built on the previous study, adding data from teenagers 13 to 16.5 years of age. All participants had an IQ of at least 80 and were being raised by their biological mothers. They did not have any neurological, psychiatric or learning disorders.

The researchers recorded the teens’ mothers saying three nonsense words, which lasted just under a second. Using nonsense words ensured that the participants would not respond to the words’ meaning or emotional content. Two women unfamiliar with the study subjects were recorded saying the same nonsense words. Each teenage participant listened to several repetitions of the nonsense-word recordings by their own mother and the unfamiliar women, presented in random order, and identified when they heard their mom. Just like younger children, teens correctly identified their mothers’ voices more than 97% of the time.

The teens were then placed in a magnetic resonance imaging scanner, where they listened again to the voice recordings. They also listened to brief recordings of household sounds, such as a dishwasher running, to allow the researchers to see how the brain responds to voices versus other non-social sounds.