A key to understanding social communication deficits in autism spectrum disorders: Neural processing of sound and speech intonation

Autism spectrum disorders (ASD) is a highly heterogeneous and pervasive developmental disorder that affects nearly 1 in 150 children. A primary indicator of ASD is behavioral language impairment with respect to social communication, but the neurophysiology behind this impairment is not well understood. Both the perception and production of prosody is impaired in children with ASD. A major acoustic cue of prosody is the variation in vocal pitch (fundamental frequency) contour which helps in the perception of emotion and intention when someone is speaking. This study investigated children with and without ASD in order to describe the relationship between the language impairment in ASD and speech-evoked auditory potentials (recorded from the brainstem and cortex) and auditory-vocal regulation of voice fundamental frequency. Brainstem responses were evaluated in response to a consonant-vowel syllable /da/ and fully voiced speech syllables /ya/ with variable pitch contours. Cortical data were collected in response to the speech syllable /da/. Finally, control of voice fundamental frequency was examined using an auditory feedback/pitch-shift reflex paradigm. This study is the first demonstration of abnormal speech-evoked auditory brainstem responses in children with ASD. Further, it isolated a subset of children with ASD who exhibited brainstem deficits specific to pitch tracking, which may be related to behavioral problems with prosody. Cortical responses revealed that abnormal encoding of speech in quiet in children with ASD is comparable to the encoding of speech in background noise in TD children. Finally, this study demonstrated two mechanisms of abnormal audio-vocal system regulation of voice fundamental frequency in children with ASD. Relationships between physiology and core and receptive language abilities were also established. Taken together, these data provide objective measures of neural processing deficits in ASD which may be related to the severity of the language impairment and may inform future objective sub-classification of children on the autism spectrum. Further, due to the malleability of the brainstem and cortex, it is conceivable that these methods could be utilized in the identification of children who would be ideal candidates for auditory or music-related remediation programs or used to monitor the progress of children enrolled in such therapies.