Subject: Re: Cochlea Amplifier models : a new list From: Martin Braun <nombraun@xxxxxxxx> Date: Thu, 11 Oct 2007 15:18:13 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Richard F. Lyon asked: >>>Where should I look to study the data on this idea that underlies your >>>modeling approach? >> >>You can take any data on level dependence of neural responses. None of >>them mirrors the half-octave shift of BM tuning. > > I've looked at lots of data, and you must be interpreting it differently > from how I am. So if you have something specific that we can look at and > discuss, we can try to resolve that difference. Lacking that, I'll stick > with Ruggero's interpretation that says mechanical and neural are > essentially the same, not different. OK, here it goes. 1) Mario Ruggero only compared mechanical and neural behavior at threshold. Had he compared mechanical and neural behavior at high sound levels, he would have seen the striking dissociation between the two. 2) The mechanical data (basilar membrane BM): The literature is full of data showing the half octave shift of BM behavior between low/medium sound levels and high sound levels. A freely available, and recent, example is this one: Fig. 1A of http://www.pnas.org/cgi/content/full/97/22/11744 Here we see that, at one single recording location, the BM reacted most strongly to sound levels of 0, 20, and 40 dB, when the probe tones had a frequency 9.5 kHz. At a sound level of 100 dB, however, the BM reacted most strongly, when the probe tones had a frequency 6 kHz. Interpretation: The low level data reveal the tuning of the outer hair cells (OHC), whose motility primarily excites the adjacent inner hair cells (IHC) and secondarily, as a side effect, cause local BM excursions. The high level data reveal the tuning of the BM proper, the passive BM. The protective effect of this passive BM tuning: high level sound of 9.5 kHz vibrates the BM *basalward* of the place of the OHCs tuned to 9.5 kHz. This takes out energy at the most critical frequency (9.5 kHz) that otherwise might damage the OHCs. 3) The neural data (auditory nerve fiber): If neural data would correspond to BM data, the figure above would have a corresponding figure, where the fiber fired most strongly at sound levels of 0, 20, and 40 dB, when the probe tones had a frequency 9.5 kHz, but most strongly at sound levels of 100 dB, when the probe tones had a frequency 6 kHz. Now - and this is the crucial point - such figures do not exist. Did they exist, you can be certain that Mario Ruggero would have published one, together with the figure above. The experiments were done, and the figures were plotted. But they do NOT show a parallel to BM behavior. Actually, I know that Mario is aware of these figures! For an example, take Fig. 7B in this paper: http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=4215872&ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum Here we see that at one single auditory nerve fiber recording site the firing rate was strongest at the lowest sound levels of 40 and 50 dB, when the probe tones had a frequency 6 kHz. At a sound level of 100 dB the firing rate was *again* strongest, when the probe tones had a frequency 6 kHz. Most interestingly, the data for the 100 dB probe tones show a second peak at 5.2 kHz. So, the neural data mainly reflect the OHC tuning, and secondarily also reflect the passive BM tuning. At following stages of neural processing these secondary peaks are then filtered out by lateral inhibition. 4) Conclusion: The dissociation of BM tuning and auditory nerve fiber tuning is perfect and obvious, and it has a physiological explanation. It is one of the many pieces of evidence that demonstrate the *real* function of BM mechanics. I hope these data can be of use. I would appreciate if Richard F. Lyon, or somebody else from the list, could check the referenced data and confirm for the list that they are real. Martin --------------------------------------------------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden web site: http://w1.570.telia.com/~u57011259/index.htm ----- Original Message ----- From: "Richard F. Lyon" <DickLyon@xxxxxxxx> To: <AUDITORY@xxxxxxxx> Sent: Wednesday, October 10, 2007 9:55 PM Subject: Re: Cochlea Amplifier models : a new list > At 5:39 PM +0200 10/10/07, Martin Braun wrote: >>>I haven't been able to find the evidence for the assertion that neural >>>tuning remains unchanged in some way that differs from the sense in which >>>BM tuning remains unchanged; >>[.......] >>>Where should I look to study the data on this idea that underlies your >>>modeling approach? >> >>You can take any data on level dependence of neural responses. None of >>them mirrors the half-octave shift of BM tuning. > > I've looked at lots of data, and you must be interpreting it differently > from how I am. So if you have something specific that we can look at and > discuss, we can try to resolve that difference. Lacking that, I'll stick > with Ruggero's interpretation that says mechanical and neural are > essentially the same, not different. > > Dick