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Autism is a behavioral disorder that affects communication and social interactions. One of the earliest signs of autism, which is usually diagnosed at around the age of three, is the inability to communicate with others. According to a new study, the lack of conversations could be due to how the brain interprets human voices and emotional cues. For healthy children, hearing human voices generates a pleasurable response associated with reward. The researchers found that in autistic children, however, due to poor brain wiring, human voices are not pleasurable.

"Weak brain connectivity may impede children with autism from experiencing speech as pleasurable," said Vinod Menon, Ph.D, senior author of the study reported by Medical Xpress. Menon is a professor of psychiatry and behavioral sciences at Stanford University and a member of the Child Health Research Institute at Lucile Packard Children's Hospital. "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."

The researchers compared two sets of functional magnetic resonance imaging brain scans. The first set of images was from 20 autistic children who had high-functional types of autism. These children had IQ (intelligence quotient) scores within the normal range and could speak and read normally. They did have difficulty with picking up on emotional cues however. The other set of images was taken from 19 healthy children. The researchers specifically looked at the voice-selective cortex from both regions of the brain. On the left side, they found that the cortex was weakly connected to the nucleus accumbens and to the ventral tegmental, regions that are associated with dopamine. On the right side, the researchers found a weak connection between the cortex and the amygdala, which is responsible for processing emotions.

"The human voice is a very important sound; it not only conveys meaning but also provides critical emotional information to a child," said study's lead author, Daniel Abrams, Ph.D, a postdoctoral scholar in psychiatry and behavioral sciences. "We are the first to show that this insensitivity may originate from impaired reward circuitry in the brain."

The researchers hope that their findings could help find new ways of treatment for autism. The findings were published in the Proceedings of the National Academy of Sciences.