The human voice appears to trigger pleasure circuits in the brains of typical kids, but not children with autism, a Stanford University team reports. The finding could explain why many children with autism seem indifferent to spoken words.
The Stanford team used functional MRI to compare the brains of 20 children who had autism spectrum disorders and 19 typical kids. In typical kids there was a strong connection between areas that respond to the human voice and areas that release the feel-good chemical dopamine, says Vinod Menon of the Stanford University School of Medicine. But "the strength of this coupling is reduced in children with autism," he says.
Connections between voice areas and areas involved in emotion-related learning also were weaker, Menon says. And he says the weaker the connections, the more trouble a child had communicating.
The results were reported in the Proceedings of the National Academy of Sciences.
Children with autism may not have the same motivation as other kids to listen to voices and to figure out what the words mean, Menon says.
Researchers have noted autistic children's indifference to human voices since the psychiatrist Leo Kanner described the disorder in the 1940s. But they have struggled to identify an underlying cause.
The new study's suggestion that motivation is the problem could explain why speech often comes late to children with autism even though the brain circuit involved in processing spoken words seems to function normally, says Coralie Chevallier, who studies communication in children with autism at The Children's Hospital of Philadelphia. She was not involved in the study. "It really looks like it's not that the circuit is broken, but rather that it's not spontaneously made use of" because the brain provides no reward, she says.
The results also support a theory that children with autism lack a wide range of social skills because they simply aren't as motivated as other kids to acquire them, Chevallier says. And she says if motivation is the problem, then many autism therapies are right to offer food or other tangible rewards to children when they do things like listen carefully.
"When you're reinforcing the child's behavior with M&Ms, or a piece of cookie," she says, "you're providing an extrinsic reason for the child to do something they didn't want to do in the first place. So you're working on motivation."
The new study offers a stark reminder of just how different the world can be for people with autism, says Nancy Minshew of the University of Pittsburgh. The world is filled with all kinds of sounds that a typical brain can filter out so we can pay attention to spoken words. "But in autism, that's not happening," she says.