Subject: Re: Cochlear travelling wave. An epiphenomenon? From: Neil Todd <TODD(at)FS4.PSY.MAN.AC.UK> Date: Thu, 6 Jul 2000 16:21:10 GMTDear Andrew and List Just on a point of clarity >Thankyou for reminding us that there are good reasons for believing the TW >in amphibians isn't necessary. I presume you meant to say that I was reminding you that a basilar membrane (BM) isn't necessary to set up a TW, since this structure is not present in the amphibian ear, yet both the amphibian papilla and sacculus show a TW property, thus pointing to the interaction between the OHCs and tectorial membrane in mammals as the origin of the TW (that's if you think evolution should be consistent). Neil >From: "Andrew Bell" <bellring(at)smartchat.net.au> >To: <AUDITORY(at)LISTS.MCGILL.CA> >Cc: "Neil Todd" <TODD(at)fs4.psy.man.ac.uk> >Subject: RE: Cochlear travelling wave. An epiphenomenon? Re: Cochlear tr >Date: Thu, 6 Jul 2000 18:35:42 +1000 >Importance: Normal > >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). > >