June 18, 2013
For Autistic Kids, Brain’s Reward Center Poorly Connected With Voices And Emotion
April Flowers for redOrbit.com - Your Universe Online
Regions of the brain tailored to respond to human voices are poorly connected to reward-processing circuits in autistic persons, according to a new study led by Stanford University School of Medicine. These findings, published in Proceedings of the National Academy of Sciences, could help to explain why children with autism struggle to grasp the social and emotional aspects of human speech."Weak brain connectivity may impede children with autism from experiencing speech as pleasurable," said Vinod Menon, professor of psychiatry and behavioral sciences at Stanford and a member of the Child Health Research Institute at Lucile Packard Children's Hospital.
"The human voice is a very important sound; it not only conveys meaning but also provides critical emotional information to a child," said Daniel Abrams, a postdoctoral scholar in psychiatry and behavioral sciences. According to Abrams, insensitivity to the human voice is a hallmark of autism. Abrams added, "We are the first to show that this insensitivity may originate from impaired reward circuitry in the brain."
Children with a high functioning form of autism were the focus of the study. The participants had difficulty holding a back-and-forth conversation or understanding emotional cues in another person's voice, despite having IQ scores in the normal range and being able to speak and read.
The team compared functional magnetic resonance imaging (fMRI) brain scans from 20 high functioning autistic children with the scans of 19 typically developing children. The scientists paid particular attention to a portion of the brain that responds selectively to the sound of human voices. Previous research revealed adults with autism had low voice-selective cortex activity in response to speech. Until the current study, however, no one had examined the connections between the voice-selective cortex and other brain regions in individuals with autism.
Menon and his colleagues found 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 in response to rewards in autistic children. The voice-selective cortex on the right side of the brain, which specializes in detecting vocal cues such as intonation and pitch, also had weak connections to the amygdala, which processes emotional cues.
The team found that the weaker such connections were in children with autism, the worse their communication deficits. By looking at the degree of impairment in these brain connections, the team was able to accurately predict the children's scores on the verbal portion of a standard test of autism severity.
Jennifer Phillips, a clinical associate professor of psychiatry and behavioral sciences at Stanford who also treats children with autism at Packard Children's, says the study findings may help to validate some autism therapies already in use. Pivotal response training, for example, seeks to increase social use of language in children who can speak some words but who usually do not talk to others.
"Pivotal-response training goes after ways to naturally motivate kids to start using language and other forms of social interaction," Phillips said. She suggests future research could test whether brain connections leading from voice to reward centers are strengthened by autism therapies.
A long-standing debate about why individuals with autism show little interest in human voices might also be resolved by the study´s findings. Two competing theories were examined to explain the phenomenon. One theory posits individuals with autism have a deficit in social motivation, while the second suggests they have sensory-processing deficits which impair their ability to fully hear human voices. According to the study, normal connections between voice-selective cortex and primary auditory brain regions in children with high-functioning autism suggest these children do not have sensory-processing deficits.
The team´s next steps include examining the consequences of the weak voice-to-reward circuit in autism. "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," Menon said. "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."