It has been known for more than fifty years that children with autism spectrum disorder (ASD) often appear indifferent to human voices, but it has not been known why. New study findings by Brain & Behavior Research Foundation NARSAD Grantee Vinod Menon, Ph.D., of Stanford University School of Medicine and colleagues, show that core brain circuits that relay the human voice to reward pathways are aberrant in autism, impeding children from receiving the usual reward signals associated with the human voice. The findings were published June 17, 2013 in Proceedings of the National Academy of Sciences.
"Weak brain connectivity may impede children with autism from experiencing speech as pleasurable," explains Dr. Menon, Professor of Psychiatry and of Behavioral Sciences and the study’s senior author. "It is likely that children with autism don't attend to voices because they are not rewarding or emotionally interesting, impacting the development of their language and social communication skills. We have discovered an aberrant brain circuit underlying a core deficit in autism; our findings may aid the development of new treatments for this disorder."
Functional Magnetic Resonance Imaging (fMRI) scans from 20 children with milder forms of ASD who had some difficulty with voice response were compared to scans from 19 children without the disorder. Prior research had shown that adults with ASD had low voice-selective cortex activity in response to speech. But until this study, no one had looked at connections between the voice-selective cortex and other brain regions in individuals with ASD. The new study found that in children with a high-functioning form of autism, the voice-selective cortex on the left side of the brain was weakly connected to the nucleus accumbens and the ventral tegmental area―brain structures that release dopamine, a “feel good” chemical in the brain―in response to rewards. The voice-selective cortex on the right side of the brain, which specializes in detecting vocal cues such as intonation and pitch, was weakly connected to the amygdala, which processes emotional cues.
The new findings will help adapt treatments appropriately now that it has been demonstrated that the lack of response to voice is not a sensory deficit in children with high-functioning ASD (the researchers found normal connections between voice-selective cortex and primary auditory brain regions) but rather a reward and motivational deficit.