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Neural Plasticity
Volume 2016, Article ID 3734646, 11 pages
Research Article

Midbrain Frequency Representation following Moderately Intense Neonatal Sound Exposure in a Precocious Animal Model (Chinchilla laniger)

1Department of Physiology, University of Toronto, Toronto, Canada M5S 1A8
2Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Canada M5S 3G9
3The Auditory Science Laboratory, Program in Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Canada M5G 1X8
4Department of Otolaryngology–Head and Neck Surgery, University of Toronto, Toronto, Canada M5G 2N2

Received 2 May 2016; Accepted 28 September 2016

Academic Editor: J. Michael Wyss

Copyright © 2016 Lisa M. D’Alessandro and Robert V. Harrison. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Auditory brain areas undergo reorganization resulting from abnormal sensory input during early postnatal development. This is evident from studies at the cortical level but it remains unclear whether there is reorganization in the auditory midbrain in a species similar to the human, that is, with early hearing onset. We have explored midbrain plasticity in the chinchilla, a precocious species that matches the human in terms of hearing development. Neonatal chinchillas were chronically exposed to a 2 kHz narrowband sound at 70 dB SPL for 4 weeks. Tonotopic maps in inferior colliculus (central nucleus) were defined based on single neuron characteristic frequency. We hypothesized an overrepresentation of the 2 kHz region of the maps. However, we observed a significant decrease in the proportion of neurons dedicated to the 2 kHz octave band and also away from the exposure frequency at 8 kHz. In addition, we report a significant increase in low frequency representation (<1 kHz), again a change to tonotopic mapping distant to the 2 kHz region. Thus in a precocious species, tonotopic maps in auditory midbrain are altered following abnormal stimulation during development. However, these changes are more complex than the overrepresentation of exposure related frequency regions that are often reported.