Development of an Animal Model to Study Effects of Auricular Vagal Nerve Stimulation on Brain Plasticity and Auditory Learning of Complex Phoneme Discrimination – A Preliminary Study

Neural Systems Laboratory, Institute for Systems Research, University of Maryland, College Park, Maryland, USA Laboratoire des Systèmes Perceptifs, Department of Cognitive Studies, École Normale Supérieure, Paris, France Visiting Scholar, Center for Neural Science, New York University, New York City, New York, USA

During the acquisition of spoken language, children learn to distinguish different acoustic stimuli, acquire the phonemes that form the building blocks of language, and associate the combinations of these sounds with meaning. Some of the basic underlying components of auditory discrimination and learning can be studied in animal models. For the first time, we developed a new behavioral paradigm and trained ferrets to discriminate Mandarin Chinese tonal phonemes (a total of eight “tonemes”). In order to discover whether auditory learning could be accelerated, we describe preliminary experimental results using vagal nerve stimulation (VNS) as a tool to explore the role of brain neuromodulators (released by VNS) in enhancing the process of learning complex auditory tasks, including discrimination of Mandarin Chinese tonal phonemes. Previous studies have shown that VNS activates the vagal nerve and that this activation causes the release of brain neuromodulators acetylcholine, norepinephrine and serotonin, all known to modulate attention and synaptic plasticity. We examined the effects of VNS from a dual perspective: both behavioral (task acquisition and performance) and neural (brain activity and plasticity). Our experiments specifically assessed whether stimulation of the external ear concha (auricular VNS or a-VNS), when paired with behavioral training on a complex auditory task, enhanced task acquisition and/or performance. Behavioral data on several auditory tasks in control ferrets (that did not receive a- VNS) provided a baseline for comparison with animals trained with a-VNS. Our initial, preliminary results indicate that the learning speed and performance level of ferrets in the control (no-VNS) group and the a-VNS group were not significantly different. However, although we did not find behavioral improvements from a-VNS, we did observe striking effects of a-VNS on neural responses in the primary auditory cortex (A1) of task-naïve ferrets, indicating that the neural representation of sound can be re-shaped, even by brief episodes of VNS.

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