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Re: Cochlear travelling wave. An epiphenomenon? Re: Cochlear tr
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?
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
> Andrew Bell
> -----Original Message-----
> From: AUDITORY Research in Auditory Perception
> [mailto:AUDITORY@LISTS.MCGILL.CA]On Behalf Of Neil Todd
> Sent: Friday, 30 June 2000 7:34
> To: AUDITORY@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
> 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
> 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.
> Neil Todd
> Lewis, E.R. and Lombard, R.E. In Fritzsch, B., Ryan, M.J., Wilcynski, W.,
> 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