Subject: Re: mechanical cochlear model From: "reinifrosch@xxxxxxxx" <reinifrosch@xxxxxxxx> Date: Sun, 7 Mar 2010 11:31:49 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Hello Martin, Today I partially agree with you. The measured instantaneous-frequency-versus- time curves of click-evoked BM responses [e.g., Recio and Rhode (2000), JASA 108, 2281-2298, chinchilla] indeed imply that the low-frequency components of the click propagate through the basal part of the cochlear channel not via a slow travelling wave starting at the base but via a fast liquid-compression wave. I still believe, however, that the slow travelling wave plays an important part at high frequencies. The hydrops cases that are mentioned in the references which you have given concern low frequencies. As you know, the liquid motion in a high-frequency (i.e., short-wavelength) cochlear travelling wave is spatially restricted to two regions just "above" and "below" the (narrow) BM. The round window, at the "floor" of the "lower" cochlear half-channel, is not involved; its blockage does not prevent the travelling wave. Reinhart Frosch, Dr. phil. nat., r. PSI and ETH Zurich, Sommerhaldenstr. 5B, CH-5200 Brugg. Phone: 0041 56 441 77 72. Mobile: 0041 79 754 30 32. E-mail: reinifrosch@xxxxxxxx . ----Ursprüngliche Nachricht---- Von: nombraun@xxxxxxxx Datum: 06.03.2010 21:29 An: <AUDITORY@xxxxxxxx> Betreff: Re: mechanical cochlear model While the cochlear traveling wave has appeared in numerous empirical reports on real physical models and real biological animals, it's function in hearing is not yet universally appreciated. Some people still think that it provides the well known frequency selectivity that we observe in the auditory nerve. This view, however, has been proved wrong by multiple direct experimental evidence. Just consider two bodies of evidence: 1) Hearing sensitivity is not affected, when endolymphatic hydrops presses the basilar membrane flat upon the bony cochlear wall of the scala timpani: http://www.neuroscience-of-music.se/Nageris.htm http://www.neuroscience-of-music.se/Xenellis.htm 2) It is a well established observation for more than 50 years that closure of the round window does not affect hearing sensitivity. This means that a pressure difference across the basilar membrane and a resulting traveling wave cannot be a necessary condition of hair cell excitation. Recently, Perez et al. (2009) reported that closure of the round window not only leaves hearing sensitivity unchanged but increases cochlear vulnerability at high sound levels. This second new observation is a further compelling indication as to the real function of the cochlear traveling wave. http://www.neuroscience-of-music.se/Sohmer.htm Martin --------------------------------------------------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden email: nombraun@xxxxxxxx web site: http://www.neuroscience-of-music.se/index.htm