Subject: Re: Cochlear travelling wave. An epiphenomenon? Re: Cochlear tr From: Jont Allen <jba(at)RESEARCH.ATT.COM> Date: Sun, 9 Jul 2000 15:47:34 +0200All, I think we need a new email list to discuss such issues. The auditory mailing list is the the best forum, IMO. Dan (Ellis) can you set this up for us? Jont Andrew Bell wrote: > > Dear Neil and List: > > Thankyou for reminding us that there are good reasons for believing the TW > in amphibians isn't necessary. These cases are instructive, for they can > help us gauge what conditions are necessary for setting up a TW. > > It is of particular interest that the crocodile ear and that of many birds > incorporates a 'cochlear shunt' - in particular, a hole through the basilar > membrane at the oval-window end called the ductis brevis (Kohlloffel, Hear. > Res. 13 (1984), 77-81). In some birds such as goose the duct is very wide. > In terms of TW models, it is difficult to see how the required 'differential > pressure' can be maintained, and the TW propagate, with such a short circuit > in place. > > Similar short circuits have been noted in humans. Tonndorf (Acta Oto-laryng. > 50 (1959), 171) relates a case where a person had 'open communication' > between scala vestibuli of the first turn and scala typani of the second > turn (observed post mortem), yet the person's audiogram before death showed > that hearing for frequencies below the locus of the lesion was normal. > Tonndorf also mentions cases where subjects had portions of their BM > completely ossified, but they still heard normally. > > To me, the only possible explanation of this evidence is a common-mode > pressure response of the partition. I would certainly like to hear a TW > explanation. > > Andrew Bell > > -----Original Message----- > From: AUDITORY Research in Auditory Perception > [mailto:AUDITORY(at)LISTS.MCGILL.CA]On Behalf Of Neil Todd > Sent: Friday, 30 June 2000 7:34 > To: AUDITORY(at)LISTS.MCGILL.CA > Subject: Re: Cochlear travelling wave. An epiphenomenon? Re: Cochlear tr > > Dear List > > If I may be so bold as to add an evolutionary perspective to this > fascinating > discussion. This is not at all an area of speciality of my own, but I happen > to have some familiarity with the literature due to my own interest in the > acoustic > sensitivity of the sacculus (Hear Res. 141, 180-188, 2000). If the cochlear > TW is an epiphenomenon, > it is not unique in the evolutionary history of hearing. The amphibian ear > posesses at least > four distinct end organs which have an acoustic sensitivity, two > perilymphatic structures, > the basilar papilla (BP) and the amphibian papilla (AP), and two otolith > structures, the > saccular (S) and lagena (L) maculae. Of these curiously the AP and S appear > to have a high > order TW property but the BP appears to be a simple resonance struture. > Lewis and Lombard > (1988) speculate that "If hair cells are indeed bidirectional > transducers,...., then energy > can be taken out of them by mechanical reactances, in which case, the > hair-cells themselves > could be the shunt resonances [in the critical layer resonance model]. The > tectorium of > the AP and the otoconial membrane of the saccule, could provide the > complementary reactive > coupling between the shunt resonances. We therefore have putative travelling > wave structures > in both end organs." This may have some relevance to the cochlear TW. We > should of course > exercise some caution in comparing the highly derived structures of extant > species (the > ancestral Devonian amphibian of mammals and frogs may have had hearing more > like a fish) > but the fact that the TW (epi)phenomenon has independently evolved a number > of times would > seem to lend support to the TM theory, since clearly a BM is not essential. > > Cheers > > Neil Todd > > Lewis, E.R. and Lombard, R.E. In Fritzsch, B., Ryan, M.J., Wilcynski, W., > Hetherington, > T.E., Walkowiak, W. (Eds.) The Evolution of the Amphibian Auditory System. > Wiley and Sons, > New York. (1988) > > see also > > DB Webster, RR Fay, and AN Popper (Eds) The Evolutionary Biology of Hearing. > Springer-Verlag, New York. (1992). -- Jont B. Allen AT&T Labs-Research, Shannon Laboratory, E161 180 Park Ave., Florham Park NJ, 07932-0971 973/360-8545voice, x7111fax, http://www.research.att.com/~jba