Pairing Tones with Vagus Nerve Stimulation Improves Brainstem Responses to Speech in the Valproic Acid Model of Autism.

ABSTRACT

Receptive language deficits and aberrant auditory processing are often observed in individuals with autism spectrum disorders (ASD). Symptoms associated with ASD are observed in rodents prenatally exposed to valproic acid (VPA), including deficits in speech sound discrimination ability. These perceptual difficulties are accompanied by changes in neural activity patterns. In both cortical and subcortical levels of the auditory pathway, VPA-exposed rats have impaired responses to speech sounds. Developing a method to improve these neural deficits throughout the auditory pathway is necessary. The purpose of this study was to investigate the ability of vagus nerve stimulation (VNS) paired with sounds to restore degraded inferior colliculus responses in VPA-exposed rats. VNS paired with the speech sound "dad" was presented to a group of VPA-exposed rats 300 times per day for 20 days. Another group of VPA-exposed rats were presented with VNS paired with multiple tone frequencies for 20 days. The inferior colliculus responses were recorded from 19 saline-exposed control rats, 18 VPA-exposed with no VNS, 8 VNS-speech paired VPA-exposed, and 7 VNS-tone paired VPA-exposed female and male rats. Pairing VNS with tones increased the IC response strength to speech sounds by 44% when compared to VPA-exposed rats alone. Contrarily, VNS-speech pairing significantly decreased the IC response to speech compared with VPA-exposed rats by 5%. The current research indicates that pairing VNS with tones improved sound processing in rats exposed to VPA and suggests that auditory processing can be improved through targeted plasticity.