Time course of dynamic range adaptation in the auditory nerve 1

Time course of dynamic range adaptation in the auditory nerve 1 Bo Wen, Grace I. Wang, Isabel Dean, and Bertrand Delgutte 2 Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, MA 02114, Department of Otology and 3 Laryngology, Harvard Medical School, Boston, MA 02115, Department of Electrical Engineering and Computer 4 Science and Research Laboratory of Electronics, MIT, Cambridge, MA 02139, USA, Ear Institute, University 5 College London, London WC1X 8EE, UK 6 7 Address for reprint requests and other correspondence: Bo Wen, Eaton-Peabody Laboratories, Massachusetts Eye and Ear 8 Infirmary, 243 Charles St., Boston, MA 02114 (e-mail: [email protected]). 9 10 Auditory adaptation to sound level statistics occurs as early as in the auditory nerve (AN), the 11 first stage of neural auditory processing. In addition to firing rate adaptation characterized by a 12 rate decrement dependent on previous spike activity, AN fibers show dynamic range adaptation, 13 which is characterized by a shift of the rate-level function or dynamic range toward the most 14 frequently occurring levels in a dynamic stimulus, thereby improving the precision of coding of 15 the most common sound levels (Wen et al., J Neurosci 29:13797-13808). We investigated the 16 time course of dynamic range adaptation by recording from AN fibers with a stimulus in which 17 the sound levels periodically switch from one nonuniform level distribution to another (Dean et 18 al., J Neurosci 28:6430-6438). Dynamic range adaptation occurred rapidly, but its exact time 19 course was difficult to determine directly from the data because of the concomitant firing rate 20 adaptation. To characterize the time course of dynamic range adaptation without the confound of 21 firing rate adaptation, we developed a phenomenological “dual adaptation” model that accounts 22 for both forms of AN adaptation. When fitted to the data, the model predicts that dynamic range 23 adaptation occurs as rapidly as firing rate adaptation, over 100-400 ms, and the time constants of 24 the two forms of adaptation are correlated. These findings suggest that adaptive processing in the 25 auditory periphery in response to changes in mean sound level occurs rapidly enough to have 26 significant impact on the coding of natural sounds. 27 28 adaptation; stimulus statistics; dynamic range problem; auditory nerve; anesthetized cat 29 30 31 32 Articles in PresS. J Neurophysiol (March 28, 2012). doi:10.1152/jn.00055.2012