Auditory pathway responses to parametrized vowels in autism spectrum disorders

Abstract

Autism spectrum disorder (ASD) is characterized by many behavioral symptoms, including delays in social and communicative development. A cluster of symptoms concentrate on speech and language development, especially manipulation of non-verbal information conveyed in prosody. It is largely unknown whether this is due to functional or structural differences in the brain regions involved in auditory and speech processing, although recent studies have shown that ASD individuals do exhibit different activation patterns in various brain regions in response to speech stimuli. This study investigated responses in regions of the auditory pathway to short recorded and synthesized vowel stimuli. These regions were the Inferior Colliculus, the Left Thalamus, the left Posterior Insula, the Auditory Cortex, Wernicke's area, and Broca's area. The stimuli were parametrized so as to target different signal processing capabilities associated with each region. They were presented to ASD and typically developing (TD) subjects while the salient regions were subject to a functional magnetic resonance imaging (fMRI). The results suggest that there were not gross differences in how ASD individuals responded from TD individuals in the subcortical regions. Results from the Auditory Cortex, however, showed a significant hemisphere dominance in TD subjects with more temporally complex stimuli that did not appear in ASD subjects. Moreover, the results showed that it was temporally-measured periodicities in the signal that were responsible for this difference. The results also show slightly different activation patterns in cortical regions which could have implications for attentiveness, and semantic and emotional processing. These results suggest that deficiencies in the temporal processing capabilities of the left Auditory Cortex play a major role in ASD speech processing.