Evidence indicates that children with autism spectrum disorder (ASD) have difficulty hearing and understanding speech, ranging from deafness to hypersensitivity. Several studies suggest abnormal brainstem auditory-evoked potentials in individuals with ASD.
Together, these findings led my colleagues and I to hypothesize that the hearing deficits in ASD arise from abnormal structure and function in the auditory brainstem pathway.
We studied the brainstems of individuals aged 2 to 56 years who were diagnosed with ASD in order to examine neuronal populations in the auditory brainstem. In all participants, we found significantly fewer neurons when compared with controls’ auditory brainstems, and surviving neurons were disorganized.
These studies were done on post-mortem brainstem tissue. Upon finding that these results were drastic and present in individuals as young as 2 or 3 years old, we sought to determine if any simple, non-invasive tests could help identify functional changes. We teamed with the Barber National Institute to perform a quantitative study of stapedial reflexes in a group of young patients with ASD. We found that when compared with neurotypical groups, reflexes occurred at lower thresholds (hypersensitivity), with longer latency (slower), and were asymmetric. While individual’s recordings might not have been considered abnormal, nearly all subjects with ASD had at least one recording outside the 95% confidence interval.
Our data add to the evidence of dysfunction in the auditory brainstem of patients with ASD and that these changes can be identified with simple, non-invasive tests soon after birth. This could potentially lead to early identification of children with ASD and, thus, early intervention. While such tests alone might not facilitate ASD diagnosis, they could help at least identify at-risk children. Additionally, early auditory testing may provide clinical insight into other neurodevelopmental conditions that impair hearing and language function.
Certainly, further research is needed to clarify the range of auditory dysfunction in ASD, as well as the utility of simple, non-invasive tests in identifying at-risk children.
Smith A, Storti S, Lukose R, Kulesza R. Structural and Functional Aberrations of the Auditory Brainstem in Autism Spectrum Disorder. J Am Osteopath Assoc. 2019;119(1):41-50. Available at http://jaoa.org/article.aspx?articleid=2720605.