Oscillatory Neural Responses to Speech and Nonspeech Sounds in a Nonverbal Child with Autism

Background:  EEG and MEG are widely used in studies of auditory processing in Autism Spectrum Disorders (ASD). However, for practical reasons, research has been restricted primarily to high-functioning children and adults and little is known about the neural processing of auditory stimuli in the most profoundly affected individuals. Within ASD, language skills vary widely. As a result of limited research in children with ASD without language, very little is known about the neural correlates of language in this population.

Objectives:  

The current study used Magnetoencephalography (MEG) to investigate neural responses to speech and nonspeech stimuli in a nonverbal child with Autism.

Methods:  

The case was a single 8-year-old autistic child, AA. AA was diagnosed with Autism on the Autism Diagnostic Observation Schedule (ADOS) and was below basal on the cognitive and language tests administered. AA is nonverbal and communicates via symbols on the iPad.

Brain responses to speech and nonspeech stimuli played binaurally were recorded using 160-channel MEG while the child watched a silent DVD. Speech stimuli were natural /a/ sounds, while nonspeech stimuli were complex tones consisting of sine waves that were carefully matched to the first three formants of /a/, and void of the fundamental frequency that gave it 'speechiness'. The child’s brain responses were compared to those of 29 typically developing children and verbal autistic children (ages 7-13) undergoing the same procedures.

Results: AA showed a very clear and strong evoked response to nonspeech stimuli, compared to speech stimuli. This was reflected in strong increase in alpha (8-12Hz) and low beta (13-30Hz) power post-stimulus as well as alpha phase-locking in the left hemisphere. This pattern of results was not found in any of the typically developing children or verbal autistic children. In contrast, AA’s brain responses to speech stimuli were hardly visible. Again, this was strikingly different to the other 29 participants.

Conclusions:

The present case study provides unique insight into the relationship between auditory processing in the brain and language impairment in children with ASD.  Results from the main study involving 15 typically developing and 15 ASD children will also be presented, comparing individual differences in neuromagnetic responses to the degree and nature of language impairment (as measured on performance on tests of language and social communication).