Using the Vagus Nerve to Help Hearing

Given its key role in sending or mediating sensory information throughout the body to the brain, the vagus nerve has long interested researchers as a target for potential intervention for myriad conditions. Such research has paid off. To date, research on the efficacy of stimulating the vagus nerve has resulted in approval by the Food and Drug Administration (FDA) for the treatment of drug-resistant epilepsy and depression in patients older than 12 years. A broader role for vagus nerve stimulation (VNS) is suggested by ongoing research for conditions such as pain, migraines, chronic inflammatory conditions, and post-stroke recovery
(J Inflamm Res. 2018;11:203–213).

Another potential role may be for improving auditory processing. A number of preclinical and small pilot studies in humans show a potential for pairing VNS with tones to improve auditory processing, such as for patients with tinnitus. Data show that VNS paired with specific tones improved the tinnitus percept in a rat model and reversed the abnormal primary auditory cortex plasticity linked to tinnitus (Nature. 2011;470:101–104). Subsequent pilot clinical studies looked at the feasibility and safety of VNS paired with tones in patients with moderate-to-severe chronic tinnitus (Neuromodulation. 2014;17:170–179; Sci Rep. 2017;7:11960). These studies found that 50% of patients in the VNS-tone paired group showed clinically meaningful improvements in their tinnitus, compared with 28% in the control group after six weeks of treatment.

Now new preclinical research recently reported by researchers at the University of Texas in Dallas shows that this VNS-induced plasticity does not occur only in the primary auditory cortex, but is more widespread and occurs across multiple areas within the auditory pathway (J Neurophysiol. 2019;122:659-671). Building on prior research that focused on VNS-tone pairing therapy in the context of tinnitus, the new research used VNS-tone pairing therapy in rats with normal hearing to examine the neural response to VNS-tone therapy on subcortical and cortical auditory fields.

Although the results are preliminary, the authors suggest that the multiple changes in the auditory pathway found after VNS-tone therapy in their rat model provides a framework for future preclinical and clinical studies.

The study demonstrated that pairing VNS and tones increased both cortical and subcortical plasticity. “Stimulation of the vagus nerve activates neuromodulator release in the brain, and this neuromodulator release paired with sound presentation generates plasticity throughout the auditory system, both cortically and subcortically,” said the study’s senior author, Crystal T. Engineer, PhD, a research assistant professor at The University of Texas at Dallas. “In the current study, we paired vagus nerve stimulation with the presentation of tone and found that the neural representation of the paired sound was enhanced in four auditory fields: the inferior colliculus, the primary auditory cortex, the anterior auditory field, and the posterior auditory field.”

According to Dr. Engineer, the novelty of this research is that pairing VNS and sound presentation has the ability to alter both early and late levels of the auditory pathway. “By pairing VNS with a sound, we are able to manipulate auditory responses specifically to the paired sound, which opens doors to a variety of new therapeutic tools for individuals with auditory processing disorders,” she said.

Although preliminary, the authors suggest that the multiple changes in the auditory pathway found after VNS-tone therapy in their rat model provide a framework for future preclinical and clinical studies.