International Meeting for Autism Research (London, May 15-17, 2008): BRAINSTEM TRANSCRIPTION OF SPEECH IN AUTISM SPECTRUM DISORDERS

Friday, May 16, 2008

Champagne Terrace/Bordeaux (Novotel London West)

N. M. Russo , The Roxelyn and Richard Pepper Department of Communication Sciences; Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL

B. L. Trommer , Pediatrics and Neurology; Feinberg School of Medicine, Interdepartmental Neuroscience Program; Evanston Northwestern Hospital Center for Neurodevelopmental Disabilities, Northwestern University, Evanston, IL

E. E. Skoe , The Roxelyn and Richard Pepper Department of Communication Sciences, Northwestern University, Evanston, IL

T. G. Nicol , The Roxelyn and Richard Pepper Department of Communication Sciences, Northwestern University, Evanston, IL

S. G. Zecker , The Roxelyn and Richard Pepper Department of Communication Sciences, Northwestern University, Evanston, IL

A. R. Bradlow , Department of Linguistics; Interdepartmental Neuroscience Program, Northwestern University, Evanston, IL

J. M. Hornickel , The Roxelyn and Richard Pepper Department of Communication Sciences, Northwestern University, Evanston, IL

N. Kraus , The Roxelyn and Richard Pepper Department of Communication Sciences; Interdepartmental Neuroscience Program; Department of Neurobiology and Physiology and Department of Otolaryngology, Northwestern University, Evanston, IL

Background: Language impairment is a hallmark of autism spectrum disorders (ASD) and prosody, represented by pitch contour of speech, is particularly affected. Prior investigations of language representation in ASD have detected deficiencies in speech perception and cortical encoding, but information about lower (brainstem) level processing is lacking. The fidelity of brainstem transcription permits a link between the acoustic components of speech (e.g., consonants/vowels/pitch) with distinct aspects of the evoked response (e.g., timing/frequency information).

Objectives: To determine whether the auditory brainstem responses to speech syllables in children with ASD differ in comparison with typically developing (TD) controls.

Methods: Speech stimuli, including a consonant-vowel speech syllable /da/ and two fully voiced /ya/ syllables, with ascending and descending pitch contours, were delivered monaurally to the right ear to children (7-13 years) with ASD (N=21) and age- and IQ-matched TD children (N=18). All subjects had normal hearing by air threshold audiometry (20 dB HL) and click-evoked wave V latency and normal mental ability.

Results: /da/-evoked potentials showed altered representation of stimulus timing and frequency, reduced fidelity to stimulus, and greater degradation by noise in ASD vs. TD (p < 0.05). A subset of the ASD group (N=5) also showed reduced phase locking and pitch tracking in response to /ya/ (p < 0.02). A limited number (3/6) of ASD subjects who underwent auditory training demonstrated improved brainstem transcription of speech, whereas ASD subjects without training (N=6) had stable responses over time.

Conclusions: These data provide unique evidence of deficient brainstem processing of speech sounds in ASD, and suggest a relationship between aberrant prosody and impaired subcortical pitch tracking. Because the speech-evoked auditory brainstem response is both passively-elicited and malleable, it may have clinical utility in detection of ASD as well as monitoring responses to intervention.

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