Subject: Re: Cochlea Amplifier models : a new list From: "reinifrosch@xxxxxxxx" <reinifrosch@xxxxxxxx> Date: Fri, 19 Oct 2007 19:39:09 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Hello Dick, Matt, and List, Today, too, I shall reply to your points later, with the exception of Matt's first question on "the point I am trying to make". As probably many list members have guessed, my main point is the presentation and discussion of a specific cochlear model, which very probably is not new, but which for shortness I shall now call "my model": 1) There are "BM resonators" (spring = BM fibres, mass = organ of Corti). 2) There are "HC (Hensen-cell) resonators" (spring = OHC's and maybe parts of Deiters cells, mass = Hensen cells and other nearby structures; the RL pivots around the apex of the pillar cells and thus varies the angle which it forms with the BM). 3) At any given location on the BM, the resonance frequency of the HC resonator is lower, by about one octave, than that of the BM resonator. 4) x_b = distance, on BM, from base. During a soft or medium-loud sine tone, the HC resonators basal of the basal limit of the active-peak x_b-region are not excited significantly, because their resonance-peak frequency region is above the sine-tone frequency. The OHC's in that basal x_b-region do not feed energy into the travelling wave (TW) and thus are "passive". In a short x_b-region above the just mentioned x_b limit, the sine-tone frequency is within the resonance-peak frequency region of the HC resonators; these resonators are excited, and the OHC's, by their motor proteins, feed energy into the TW. At locations with x_b above the active-peak centre, the resonance frequency region of the HC resonators is below the sine-tone frequency, and the OHC's feed no energy into the TW. Now I would like to encourage interested list members to go to the library and look at some more figures in journals which in my opinion are consistent with "my" model: 1) A. Fridberger and J. Boutet de Monvel (2003), "Sound- induced differential motion within the hearing organ", nature neuroscience 6, 446-448. Figs. 2b and 2d show that the rotation centres of the guinea-pig cochlear-explant RL and TM during 160-Hz sine-tones did not coincide in space, but were separated from each other by about 0.05 mm. The RL rotation centre was close to the IHC's, and the BM rotation centre was either at the feet of the inner pillar cells or under the nerve fibres contacting the IHC's. The observed place was near the 160-Hz characteristic place. The sound was very loud (126 dB SPL), but the effective level was reduced by opening of the cochlea and immersion of the preparation in tissue culture medium. Nevertheless, the energy generated by the OHC's was, because of the high level, probably not large in comparison with the energy fed to the observed region on other paths. 2) P. J. Kolston (2000), "The importance of phase data and model dimensionality to cochlear mechanics", Hearing Research 145, 25-36. Fig. 9 shows results of Paul's finite- element calculations giving a good fit to soft-sine-tone 9-kHz chinchilla BM vibration level and phase data of Ruggero et al. This Fig. 9 approximately confirms the earlier-mentioned Fig. 3 of de Boer and Nuttall (1999). In this Fig. 9, the (only) successful model is that represented by the dotted curves ("stimulus enhancement"). The real part is negative (OHC's feed energy into the TW) from x_b = 1.2 mm to x_b = 3.6 mm; the active peak (Fig. 8A) is at x_b = 3.7 mm, and the place where the imaginary part of the BM impedance vanishes (i.e., the place of the BM-resonator which has a resonance frequency of 9 kHz) is within the graph in this case, namely at x_b = 5.0 mm. The reason why no passive peak is visible in this Fig. 9 is given under point 3 below. 3) A. Recio et al. (1998), "Basilar-membrane reponses to clicks at the base of the chinchilla cochlea", JASA 103, 1972-1989. Fig. 10 shows gain-versus-frequency spectra for two animals. Here the frequency domain is used, i.e., a fixed place at about x_b = 3.7 mm is considered. Laser velocimetry and Fourier transformation were used. The sine-tone frequency in this Fig. 9 ranges from 3 to 11 kHz, and the levels for the 9 living-animal curves were 26, 36, ... , 106 dB for animal L13, and 24, 24, ... , 104 dB for animal L113. In addition, there are two post-mortem curves at 96 and 106 dB (L13), and at 94 and 104 dB (L113). Animal L13 has especially high gains. At 26, 36, 46, 56, and 66 dB, the highest peak is at 9.0 kHz. This peak is absent in the post-mortem curves and thus can be said to be the "active peak". The post-mortem curves are about equal to the 106-dB and 104-dB curves and exhibit the broad passive peak, at 6 kHz, i.e., about half an octave below the active peak. The L13-curves from 76 dB to 96 dB have their highest point at values between 6 and 9 kHz; that can be understood by looking at Fig. 9, where BM velocity (rather than gain) is shown: at 66 dB the OHC-Amplifiers generate their maximal energy. At higher levels, the height, in dB, of the active peak is reduced, so that the active peak degrades to a small spike on the high-frequency slope of the passive peak. In Fig. 10, the gain is level-independent below 6 kHz, because the resonance-peak frequency-region of the local HC resonator is above 6 kHz. Thus for frequencies below 6 kHz the TW is entirely passive from the base to the considered place of x_b = 3.7 mm. In the 26-dB curve of Fig. 10 (L13), the passive peak is not clearly visible because the low-frequency slope of the active peak starts at 6 kHz. I hope to be able to discuss the additional peak at 8.1 kHz in the L13-curves at 56 to 86 dB later. 4) A. R. Cody (1992), "Acoustic lesions in the mammalian cochlea: Implications for the spatial distribution of the 'active process' ". The right half of Fig. 2 shows results obtained with a living-guinea-pig cochlea with completely destroyed OHC's from x_b = 2 mm to x_b = 4 mm. The BM sensitivity for soft sine-tones of 23, 18 and 14 kHz was strongly reduced, but that for 13 kHz was normal. The characteristic place (i.e., the active peak) for soft 13-kHz sine-tones in guinea pigs is at x_b = 4.5 mm. So, during a soft 13-kHz sine-tone, in a healthy guinea-pig cochlea, only the OHC's located between x_b = 4.0 mm and x_b = 4.5 mm are active. Reinhart Frosch. 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: DickLyon@xxxxxxxx Datum: 18.10.2007 23:48 An: <reinifrosch@xxxxxxxx>, <AUDITORY@xxxxxxxx> Betreff: Re: Cochlea Amplifier models : a new list Matt says you are pointing out two distinct peaks. So I repeat my question from before: does the data support only that interpretation? Or can the two (active and passive) peaks be just as well interpreted as two ends of a level-dependent continuum, reflecting a degree of active involvement? Active traveling-wave models as I know them show a continuous behavior between low-level active and high- level passive, with degree of activity also influenced by efferent control and local adaptation state. Do you believe the data support that notion? Or contradict it? Or neutral? Dick