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Auditory processing delays may explain autism.

CHICAGO -- Researchers have identified delays in auditory processing in the brains of children with autism spectrum disorders.

Although the response to various sounds is delayed by only a fraction of a second, this delay may underpin the subsequent language and communication impairment seen in children with autism, principal investigator Timothy Roberts, Ph.D., reported at the annual meeting of the Radiological Society of North America.

Dr. Roberts and colleagues at Children's Hospital in Philadelphia used magnetoencephalography imaging to measure the electromagnetic field produced during neuronal activation in 30 children with autism spectrum disorders, with or without concomitant language impairment, and 34 age-matched typically developing controls.

Recordings were made using a 275-channel whole-head unit while the children were watching a silent movie of their choice without performing any tasks.

When introduced to single tones ranging in frequency from 100 Hz to 1,000 Hz, there was a strong evoked response in typically developing children and a consistent and significant delay of about 20 milliseconds in the response of children with autism.

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The delay was particularly pronounced at the midrange tones of 300-500 Hz--the frequency range where the bulk of human speech is located, Dr. Roberts said.

"This is a very critical range to be manifesting such a delay in processing sounds," he said. "It's like the signal to have a response simply doesn't get to that part of the brain on time, like when the freeway is clogged up with cars and you can't get to where you're going on time. That delay can have downstream consequences."

When the children were introduced to mismatched tones, there was a significant 35- to 50-millisecond delay in the brains of autistic children to register that one tone was different from another. The delay was most pronounced in the autistic children with language impairment, averaging 40 milliseconds slower than typically developing children. That is about 1/20 of a second, which doesn't sound like much, except that each syllable of speech lasts only about a 1/4 of a second, said Dr. Roberts, vice chair of research in the department of radiology at Children's Hospital in Philadelphia.

"To have a 50-millisecond delay in registering that a syllable has changed could be catastrophic," he said. For example, with the word "elephant," he said, "you're still dealing with the 'el' when everyone else has moved on to the 'phant." You can never catch up, and this could be catastrophic."

As for how the findings might be used in clinical practice, Dr. Roberts said that they are hoping to use brain activity patterns to establish a "suite of biomarkers" for autism that could be used to improve classification of the disorder and guide treatment.

"It may be that we start addressing the heterogeneity of the autistic population by subtyping," he said. "Based on that subtyping, one might triage these patients into different behavioral interventions. It's speculative, but it suggests that if you have an auditory processing deficit that part of your therapy ought to be working on improving auditory processing, whereas if you don't, then maybe your intervention should target something else."

In a step toward that goal, the investigators used receiver operating characteristic curves to determine if latency responses to various sounds could distinguish study participants with autism from those without the disorder.

What they found was a significant correlation between autism and the response to a single beep tone in the 500-Hz range, resulting in a sensitivity of 82% and specificity of 70%. The correlation was also significant when mismatched tones were used as stimuli, producing a sensitivity of 88% and specificity of 74%, Dr. Roberts reported.

Getting children to sit still for any kind of testing can be challenging, with recordings possible in 51 (80%) of the cohort. Their mean age was 10 years, and roughly 95% were male.

Magnetoencephalography (MEG) has typically been used for epilepsy evaluations, but is emerging as a neurologic/radiologic tool. It lends itself to disorders of connectivity such as autism or Parkinson's disease because of its ability to evaluate the timing of brain activity and the propagation of activity from one area of the brain to another, Dr. Roberts said.

"MEG gives us a reasonable idea of the spatial location of the activity, but gives us a wonderful view of the timing of it," he said.

Researchers have made a recording in an 18-month-old, and are recruiting 100 families to study the use of MEG in neonates and young children. The hope is for early intervention during the crucial stage of language development, possibly by slowing down speech to the affected child.

The study was sponsored by the National Institutes of Health and the Nancy Lurie Marks Family Foundation. The investigators reported no conflicts of interest.

To watch an interview with Dr. Roberts, go to: http:// www.youtube.com / family practicenews.

BY PATRICE WENDLING

Chicago Bureau
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Title Annotation:Mental Health
Author:Wendling, Patrice
Publication:Family Practice News
Geographic Code:1USA
Date:Dec 15, 2008
Words:809
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