Efferent inhibition strength is a Physiological Correlate of Hyperacusis in Children with Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a developmental disability that is poorly understood. ASD can influence communication, social interaction, and behavior. Children with ASD often have sensory hypersensitivities, including auditory hypersensitivity (hyperacusis). In adults with hyperacusis who are otherwise neurotypical, the medial olivocochlear (MOC) efferent reflex is stronger than usual. In children with ASD the MOC reflex has been measured, but without also assessing hyperacusis. We assessed the MOC reflex in children with ASD by measuring the strength of MOC-induced inhibition of transient-evoked otoacoustic emissions (TEOAEs), a non-invasive, physiological measure that reflects cochlear amplification. MOC activity was evoked by contralateral noise. Hyperacusis was assessed subjectively based on the children's symptoms. We found a strong correlation between hyperacusis scores and MOC strength in children with ASD. When children were divided into ASD-with-severe-hyperacusis (ASDs), ASD-with-not-severe-hyperacusis (ASDns) and neurotypical (NT) groups, the last two groups had similar hyperacusis and MOC reflexes while the ASDs group, on average, had hyperacusis and MOC reflexes that were approximately twice as strong. The MOC inhibition of TEOAEs averaged larger at all frequencies in the ASDs compared to ASDns and NT groups. The results suggest that the MOC reflex can be used to estimate hyperacusis in children with ASD and might be used to validate future questionnaires to assess hyperacusis. Our results also provide evidence that strong MOC reflexes in children with ASD are associated with hyperacusis and that hyperacusis is a comorbid condition as opposed to being an integral part of the abnormal neural processing associated with ASD.

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