Neurotypical brains, upon hearing people speak, release dopamine, rewarding the brain for listening. However, research from Stanford has found that in people with autism, the regions of the brain that process vocal information have only a weak connection to the sections of the brain that would make the experience of listening pleasurable. This study is the first to explain why people with autism react the way they do to speech and also validates some current treatment practices.

The research focused on children who exhibited high-functioning autism—meaning they had normal IQ scores and could speak and read, but they did have problems when it came to maintaining a conversation with others or understanding emotional cues. Researchers conducted functional magnetic resonance imaging (fMRI) scans on 20 such children as well as 19 neurotypical children. The researchers observed the brain to see which parts showed activity in response to speech. In particular, they investigated the connection between the voice-selective cortex and other parts of the brain.

The fMRI data revealed that the voice-selective cortex on the left side of the brain lacked a robust connection to the nucleus accumbens (a critical part of the brain’s pleasure center) and the ventral tegmental area (they key to dopamine and rewards in the brain). The section of the voice-selective cortex on the right side of the brain—responsible for detecting vocal information like intonation and pitch—shared a weak link with the amygdala (a major player in the processing of emotional responses).

The strength of the connection between the voice-selective cortex and these related segments of the brain is directly correlated with communication deficits in children with autism; the weaker the connections, the worse the communication deficits. Based on data regarding the brain’s connections in this area, the researchers could predict how well children would score on the verbal portion of a standard test of autism severity.

This research is another piece of the puzzle of understanding how autistic brains differ from neurotypical ones. The research team reports that it will next investigate the consequences of autistic brains having a weak mechanism for rewarding vocal stimuli.

The research is published in this month’s edition of the Proceedings of the National Academy of Sciences.

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