New study reveals why autistic teens struggle with sounds of unfamiliar voices

Just like other teenagers, many teens on the autism spectrum are itching to exercise their social muscles. They hope for new friends, fun with people who share their interests, maybe even a romantic relationship. 

Adolescence is a moment of opportunity for these kids. They want to build friendships."

Daniel Abrams, PhD, clinical associate professor of psychiatry and behavioral sciences, Stanford Medicine

But spreading their social wings is challenging for teens with autism. A new Stanford Medicine-led study, publishing July 13 in Proceedings of the National Academy of Sciences, sheds light on a key factor: how the brains of teenagers with autism handle the sounds of unfamiliar voices. Unlike in neurotypical teenagers, the reward centers in autistic teens' brains don't become increasingly responsive to strangers' voices as they mature, the research found.

"Typically developing teens are becoming far more aware of their social world, and tuning in to new voices is important for making new social connections," said Abrams, who led the new research as well as a 2022 study on neurotypical teens' responses to voices.

"Our results point to adolescence as a period when, for some kids with autism, their brains are not becoming increasingly responsive to unfamiliar vocal stimuli," Abrams said. "Their brains did not show an uptick in responding to new voices like the neurotypical kids did."

The study's senior author is Vinod Menon, PhD, the Rachael L. and Walter F. Nichols, MD, Professor and a professor of psychiatry and behavioral sciences. 

"We tend to think of autism in terms of what the brain does differently, but not enough about how those differences unfold with age," Menon said. "The way the brain attends to socially relevant information is reshaped throughout adolescence, and in autism that developmental process appears to follow a different course."

Young kids with autism are less attuned to voices than others their age, prior research has shown. As they reach adolescence, some teens with autism show unchanged engagement with voices, while those with the most severe autism symptoms are even less engaged than younger kids.

The researchers also examined how teens' brains respond to the sound of their mother's voice. In neurotypical teens, the sound of Mom's voice remains highly rewarding, but unfamiliar voices become increasingly engaging as adolescents mature. In contrast, teens with autism become increasingly attuned to their mother's voice, with the strongest examples of this pattern in teens with the most severe autism symptoms.

A key social sound

The voices of people around us - friends, family members, even strangers - are a key signal in human emotional bonds. (Think of the swell of happiness you feel from the sound of a loved one's voice after a long absence, or the comfort of hearing a friend's sympathetic tone if you are grieving.)

"Voices provide a really important set of cues to help us feel connected to the people we know and love," Abrams said. "But, from early stages of development, kids with autism struggle to tune into the vocal world."

Autism is a developmental disorder that affects 1 in 31 children and is characterized by social difficulties, not just with interpreting voices but also with skills such as interpreting facial expressions and maintaining eye contact as well as restricted interests, repetitive behaviors and sensory aberrations. The condition exists on a wide spectrum, with some individuals much more affected than others.

A small child's unresponsiveness to the sound of their own name can be an early clue that they have autism. And prior research by Abrams' team showed that 7- to 12-year-old children with autism have difficulty picking up emotional cues in people's voices.

However, no one had studied how brain responses to voices change during adolescence in autism.

"Autism changes over the course of a lifetime; it's not one thing," Abrams said. "The way that autism is expressed in younger kids is different than in older kids and in teenagers."

Understanding how autism manifests in teens could drive new opportunities for therapies tailored to this phase of life, he added.

Familiar and unfamiliar voices

The researchers studied 79 children and teens who were 7 to 17 years old. The group included 39 participants with autism spectrum disorder and 40 typically developing participants who were matched on age, sex and IQ to the individuals with autism.

As their brain activity was being recorded by the functional magnetic resonance imaging scanner, the study participants listened to three types of brief recordings: nonsense words such as "keebudishawlt" spoken by their mother; the same nonsense words spoken by two unfamiliar women; and non-voice environmental sounds, such as a dishwasher running. (Nonsense words were used in the voice recordings to avoid engaging parts of the brain that respond to the meanings of words.) The researchers analyzed how the brain responded to each type of sound in young people with and without autism, and how the responses varied with age.

The study produced several insights into how the adolescent brain is processing voices in autism, Abrams said.

The researchers found that "social" brain centers engaged differently depending on whether the individual had autism. In typically developing teens, the brain's reward centers and brain regions focused on salience (directing what one pays attention to) both responded more strongly to voices the older the teen was. In teens with autism, the reward and salience centers did not become more responsive to voices, and in some older individuals these brain regions were even less responsive to voices than in younger children with autism.

The research also found that teens with autism tuned in more to their mother's voice than to unfamiliar voices - the opposite of what neurotypical teenagers do.

The more impaired their social skills were, the more their brains favored the sound of their mom's voice.

"In neurotypical kids, we found a strong pattern in adolescence to tune in more to unfamiliar voices than to Mom's voice," Abrams said. "They're tuning into new social partners."

But in kids with autism, he said, "Instead of tuning into unfamiliar voices during adolescence, they were tuning in more to the sound of their mom than at younger ages. We think this pattern reflects the social communication challenges faced by many adolescents with autism."

New possibilities for treatment

The findings point to new prospects for autism therapies tailored to the characteristics of the teen brain, Abrams said.

"Autism treatments are often focused on much younger kids, with far fewer options for adolescents," he said, adding that early interventions focused on preschoolers remain critically important, but teens shouldn't be neglected.

"We know the brain is plastic and developing all the way through adolescence, in everyone," he said. "There's no question that adolescence provides a golden opportunity, especially for teens with autism who are enthusiastic about building social connections. We hope the field can translate our expanding knowledge of the brain into more effective interventions."

A researcher from the University of Zurich and ETH Zurich contributed to the study. The research was funded by the National Institutes of Health (grant K01MH102428), the Brain and Behavior Research Foundation, the Swiss National Science Foundation, and an anonymous philanthropic donation.