"Are you even listening to me?"
It's a question that discouraged parents often throw at their distracted teenagers, and the truthful answer is probably, "No."
It's hard to really blame them. New research on adolescent brains suggests the reaction we have to certain voices naturally shifts with time, making our mother's voice feel less valuable.
When scanning the brains of children, those 12 years and under showed an explosive neural response to their mother's voice, activating reward centers and emotion-processing centers in the brain.
Yet sometime around a kid's 13th birthday, a change occurs.
The mother's voice no longer generates the same neurological reaction. Instead, a teenager's brain, regardless of their sex, appears more responsive to all voices in general, whether new or remembered.
The changes are so apparent that researchers were able to guess a child's age simply based on how their brain responded to their mother's voice.
"Just as an infant knows to tune into her mother's voice, an adolescent knows to tune into novel voices," explains psychiatrist Daniel Abrams from Stanford University.
"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 suspect this is a sign of the teenage brain developing social skills. In other words, a teenager doesn't intentionally close off their family; their brain is just maturing in a healthy way.
Numerous lines of evidence have shown that for young children, a mother's voice plays an important role in their health and development, impacting their stress levels, their social bonding, their feeding skills, and their processing of speech.
So it makes sense that a child's brain would be especially in tune with the voice of their parent.
However, there comes a point when listening to people other than your mother is more advantageous.
"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," says neuroscientist Vinod Menon, also from Stanford University.
The findings build on fMRI results published by the same team of researchers in 2016, which found children under the age of 12 show brain circuits selectively engaged by a mother's voice.
When extending the study to 22 teenagers, between 13 and 16.5 years of age, however, a mother's voice didn't have quite the same impact.
Instead, all voices heard by teenagers activated neural circuits associated with auditory processing, picking out salient information and forming social memories.
When presented with a recording of their mother's voice saying three nonsense words, as opposed to a stranger's voice saying the same thing, the participants' brain scans actually showed less activation in reward centers of the brain.
The same was true of the ventromedial prefrontal cortex, which is the part of the brain that helps determine which social information is most valuable.
Researchers are hoping to look into how these brain circuits differ among those with neurological conditions.
Among younger children, for instance, researchers at Stanford have found those with autism do not show as strong a response to their mother's voice. Knowing more about the underlying neurobiological mechanisms could help us understand how social development occurs.
The findings of the current study are the first to suggest that as we get older, our hearing is focused less on our mother and more on the voices of a whole variety of people.
The idea is supported by other behavioral and neural studies, which also suggest reward centers in the adolescent brain are marked by heightened sensitivity to novelty in general.
These changes could be key parts of healthy social development, allowing teenagers to better understand the perspective and intentions of others.
"A child becomes independent at some point, and that has to be precipitated by an underlying biological signal," says Menon.
"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."
The study was published in the Journal of Neuroscience.