Auditory Brainstem Pathology in Autism Spectrum Disorder: A Review.

Atypical responses to sound are common in individuals with autism spectrum disorder (ASD), and growing evidence suggests an underlying auditory brainstem pathology. This review of the literature provides a comprehensive account of the structural and functional evidence for auditory brainstem abnormalities in ASD. The studies reviewed were published between 1975 and 2016 and were sourced from multiple online databases. Indices of both the quantity and quality of the studies reviewed are considered. Findings show converging evidence for auditory brainstem pathology in ASD, although the specific functions and anatomical structures involved remain equivocal. Two main trends emerge from the literature: (1) abnormalities occur mainly at higher levels of the auditory brainstem, according to structural imaging and electrophysiology studies; and (2) brainstem abnormalities appear to be more common in younger than older children with ASD. These findings suggest delayed maturation of neural transmission pathways between lower and higher levels of the brainstem and are consistent with the auditory disorders commonly observed in ASD, including atypical sound sensitivity, poor sound localization, and difficulty listening in background noise. Limitations of existing studies are discussed, and recommendations for future research are offered.