Original Research ARTICLE
Evidence of hyperacusis in adult rats following non-traumatic sound exposure
- 1Centre for Research on Brain Language and Music, Canada
- 2Montreal Neurological Institute and Hospital, McGill University, Canada
- 3Department of Psychiatry, Medical School, University of Minnesota, United States
- 4Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Brazil
Manipulations that enhance neuroplasticity may inadvertently create opportunities for maladaptation. We have previously used passive exposures to non-traumatic white noise to open windows of plasticity in the adult rat auditory cortex and induce frequency-specific functional reorganizations of the tonotopic map. However, similar reorganizations in the central auditory pathway are thought to contribute to the generation of hearing disorders such as tinnitus and hyperacusis. Here, we investigate whether noise-induced reorganizations are accompanied by electrophysiological or behavioral evidence of tinnitus or hyperacusis in adult Long-Evans rats. We used a two-week passive exposure to moderate-intensity (70dB SPL) broadband white noise to reopen a critical period for spectral tuning such that a second one-week exposure to 7kHz tone pips produced an expansion of the 7kHz frequency region in the primary auditory cortex (A1). We demonstrate for the first time that this expansion also takes place in the ventral auditory field (VAF). Sound exposure also led to spontaneous and sound-evoked hyperactivity in the anterior auditory field (AAF). Rats were assessed for behavioral evidence of tinnitus or hyperacusis using gap and tone prepulse inhibition of the acoustic startle response. We found that sound exposure did not affect gap-prepulse inhibition. However, sound exposure led to an improvement in prepulse inhibition when the prepulse was a 7kHz tone, showing that exposed rats had enhanced sensorimotor gating for the exposure frequency. Together, our electrophysiological and behavioral results provide evidence of hyperacusis but not tinnitus in sound-exposed animals. Our findings demonstrate that periods of prolonged noise exposure may open windows of plasticity that can also be understood as windows of vulnerability, potentially increasing the likelihood for maladaptive plasticity to take place.
Keywords: Tonotopic map reorganization, Maladaptive plasticity, Tinnitus, Hyperacusis, sound exposure, experience-dependent plasticity, Auditory Cortex, PPI, GPIAS
Received: 09 Jul 2019;
Accepted: 03 Oct 2019.
Copyright: © 2019 Thomas, Guercio, Drudik and De Villers-Sidani. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Etienne De Villers-Sidani, Centre for Research on Brain Language and Music, Montreal, Quebec, Canada, email@example.com