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The Journal of Neuroscience, November 4, 2009, 29(44):13797-13808; doi:10.1523/JNEUROSCI.5610-08.2009

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Behavioral/Systems/Cognitive
Dynamic Range Adaptation to Sound Level Statistics in the Auditory Nerve

Bo Wen,^1,2 Grace I. Wang,^1,2,3 Isabel Dean,⁴ and Bertrand Delgutte^1,2

¹Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, ²Research Laboratory of Electronics and ³Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and ⁴Ear Institute, University College London, London WC1X 8EE, United Kingdom

Correspondence should be addressed to Bo Wen, Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114. Email: bwen{at}mit.edu

The auditory system operates over a vast range of sound pressure levels (100–120 dB) with nearly constant discrimination ability across most of the range, well exceeding the dynamic range of most auditory neurons (20–40 dB). Dean et al. (2005) have reported that the dynamic range of midbrain auditory neurons adapts to the distribution of sound levels in a continuous, dynamic stimulus by shifting toward the most frequently occurring level. Here, we show that dynamic range adaptation, distinct from classic firing rate adaptation, also occurs in primary auditory neurons in anesthetized cats for tone and noise stimuli. Specifically, the range of sound levels over which firing rates of auditory nerve (AN) fibers grows rapidly with level shifts nearly linearly with the most probable levels in a dynamic sound stimulus. This dynamic range adaptation was observed for fibers with all characteristic frequencies and spontaneous discharge rates. As in the midbrain, dynamic range adaptation improved the precision of level coding by the AN fiber population for the prevailing sound levels in the stimulus. However, dynamic range adaptation in the AN was weaker than in the midbrain and not sufficient (0.25 dB/dB, on average, for broadband noise) to prevent a significant degradation of the precision of level coding by the AN population above 60 dB SPL. These findings suggest that adaptive processing of sound levels first occurs in the auditory periphery and is enhanced along the auditory pathway.

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Received Nov. 23, 2008; revised Aug. 29, 2009; accepted Sept. 5, 2009.

Correspondence should be addressed to Bo Wen, Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114. Email: bwen{at}mit.edu

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