Enhancing Speech Processing In A Rat Model Of Autism Using Vagus Nerve Stimulation

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One of the major obstacles facing individuals with autism is the inability to communicate effectively. While there are many reasons for this inability, an important component appears to be a serious deficit in the ability to process speech sounds effectively. Expensive, time-consuming behavioral interventions can improve behavioral outcomes, but many individuals undergo these interventions and still experience deficits. The development of adjunctive interventions that can increase the benefit of rehabilitation therapies is essential to improve the lives of individuals with autism spectrum disorders (ASD). We have developed a novel technique to drive robust neuroplasticity and enhance the benefits of rehabilitation. Vagus nerve stimulation (VNS) paired with the presentation of a sound triggers rapid, phasic release of plasticity promoting neuromodulators, which potentiate plasticity in the auditory network. Recent preclinical and clinical findings indicate that VNS paired with sensory or motor rehabilitative therapies can significantly enhance functional recovery compared to rehabilitative therapy alone. This proposal will evaluate whether VNS paired with auditory training can enhance the efficacy of rehabilitation in the context of autism. In utero valproic acid (VPA) exposure is a well-documented cause of autism in humans. Similar to individuals with autism, both speech discrimination ability and auditory cortical responses are impaired in VPA exposed rats. The objective of this proposal is to determine whether VNS paired with auditory training can reverse the neural and behavioral auditory processing deficits observed in VPA exposed rats. In Aim 1, we test the ability of both implanted and non-invasive VNS paired with auditory training to improve discrimination ability after prenatal VPA exposure. VPA exposed rats are significantly impaired at discriminating between speech sounds. We will evaluate discrimination accuracy in VPA or saline exposed rats undergoing VNS paired auditory training. In Aim 2, we evaluate awake behaving neurophysiological responses in auditory cortex to evaluate the VNS-dependent neural plasticity that may underlie improved auditory processing. VPA exposed rats exhibit altered auditory cortex responses compared to control rats. Previous results suggest that VNS pairing may strengthen auditory cortex responses more rapidly and to a greater degree than training alone. In Aim 3, we test the role of two neuromodulatory networks in the VNS-dependent enhancement of plasticity and sound discrimination ability in the context of VPA exposure. We will deplete cholinergic or noradrenergic afferents specifically to the auditory cortex to determine whether acetylcholine or norepinephrine depletion impairs VNS-related improvements in auditory processing. In addition to proof-of- concept evidence for clinical translation, this proposal will provide insight into the ability of plasticity-based therapies to be effective in treating ASD and lay the groundwork for more comprehensive future studies, with the goal of translating these critical first-in-animal preclinical experiments to a clinical therapy that could provide significant, tangible improvements in the lives of individuals with ASD.