Subject: Cochlear-amp From: Jonathan Tapson <Jonathan.Tapson@xxxxxxxx> Date: Thu, 18 Mar 2010 08:34:15 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>This is a MIME message. If you are reading this text, you may want to consider changing to a mail reader or gateway that understands how to properly handle MIME multipart messages. --=__Part3C16DB77.0__= Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi List =20 Warning=21 Cochlear mechanics message=21 Destroy before reading if you = have a narrow view of the auditory list subject matter... =20 Martin Braun wrote: >The gain takes place within the outer hair cells (OHCs), which are the >motors of the cochlear amplifier. The amplification of a by-passing basilar >membrane traveling wave by OHCs is physically impossible, because the motor >activity of these cells has a latency. =20 The motor activity of mammalian OHCs has been recorded at up to 79kHz.=20 (see e.g.=20 Dallos & Evans, Science 267, 2006=E2=80=932009, or Frank et al., PNAS 96, 4420=E2=80=934425.) This is more than fast enough to amplify a transient = BM wave. =20 So then the question is, can that motion be recruited fast enough?=20 There are a=20 couple of hypotheses - the Hopf bifurcation hypothesis, and the=20 parametric amplification hypothesis - which suggest that the cells are constantly active under feedback control. In degenerate parametric amplification, the driving motion does not require to be particularly well phase-locked with the input signal (see Allen & Fahey, JASA 112, p.2299, 2002 for the first description of this). =20 In the Hopf bifurcation model, the amplifier is controlled in an active state of supercritical stability, from which it diverges very rapidly in response to transient input. =20 =20 In sum: the OHCs can move fast enough to react within a fraction of a wave cycle, and they are not dependent on a recruitment signal to act, and at least one model of their dynamics suggests they react very fast to transients.=20 =20 Regards Jon Tapson=20 =20 ___________________________________________________________________________= ___________________ UNIVERSITY OF CAPE TOWN=20 This e-mail is subject to the UCT ICT policies and e-mail disclaimer published on our website at http://www.uct.ac.za/about/policies/emaildisclaimer/ or obtainable from +27 21 650 4500. This e-mail is intended only for the person(s) to whom it is addressed. If the e-mail has reached you in error, please notify the author. If you are not the intended recipient of the e-mail you may not use, disclose, copy, redirect or print the content. If this e-mail is not related to the business of UCT it is sent by the sender in the sender=27s individual capacity. ___________________________________________________________________________= __________________________ =20 --=__Part3C16DB77.0__= Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Content-Description: HTML <HTML><HEAD> <META content=3D"text/html; charset=3Dutf-8" http-equiv=3DContent-Type> <META name=3DGENERATOR content=3D"MSHTML 8.00.6001.18876"></HEAD> <BODY style=3D"MARGIN: 4px 4px 1px; FONT: 10pt Tahoma"> <DIV>Hi List</DIV> <DIV> </DIV> <DIV>Warning! Cochlear mechanics message! Destroy before reading if you = have a narrow view of the auditory list subject matter...</DIV> <DIV> </DIV> <DIV>Martin Braun wrote:<BR><BR>>The gain takes place within the outer = hair cells (OHCs), which are the<BR>>motors of the cochlear amplifier. = The amplification of a by-passing basilar<BR>>membrane traveling wave = by OHCs is physically impossible, because the motor<BR>>activity of = these cells has a latency.</DIV> <DIV> </DIV> <DIV>The motor activity of mammalian OHCs has been recorded at up to = 79kHz. (see e.g. </DIV> <DIV>Dallos & Evans, <SPAN class=3Djournalname>Science</SPAN> <SPAN = class=3Djournalnumber>267</SPAN>, 2006=E2=80=932009, or Frank et al., = <SPAN class=3Datl>PNAS </SPAN><SPAN class=3Djournalnumber>96</SPAN>, = 4420=E2=80=934425.) This is more than fast enough to amplify a = transient BM wave.</DIV> <DIV> </DIV> <DIV>So then the question is, can that motion be recruited fast enough?&nbs= p; There are a </DIV> <DIV>couple of hypotheses - the Hopf bifurcation hypothesis, and = the </DIV> <DIV>parametric amplification hypothesis - which suggest that the cells = are constantly active under feedback control. In degenerate para= metric amplification, the driving motion does not require to be particularl= y well phase-locked with the input signal (see <SPAN lang=3DEN-U= S> Allen & Fahey, JASA 112, p.2299, 2002 for the first = description of this).</SPAN></DIV> <DIV><SPAN lang=3DEN-US></SPAN> </DIV> <DIV><SPAN lang=3DEN-US>In the Hopf bifurcation model, the amplifier is = controlled in an active state of supercritical stability, from which it = diverges very rapidly in response to transient input. </SPAN></DIV> <DIV><SPAN lang=3DEN-US></SPAN> </DIV> <DIV><SPAN lang=3DEN-US>In sum: the OHCs can move fast = enough to react within a fraction of a wave cycle, and they are not = dependent on a recruitment signal to act, and at least one model of = their dynamics suggests they react very fast to transients. </SPAN></D= IV> <DIV><SPAN lang=3DEN-US></SPAN> </DIV> <DIV><SPAN lang=3DEN-US>Regards</SPAN></DIV> <DIV><SPAN lang=3DEN-US>Jon Tapson </SPAN></DIV><BR> <!--StartFragment--> =20 <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> <font face=3D"Calibri" size=3D"3">___________________________________= ___________________________________________________________=20 </font> </p> <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> =20 </p> <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> <font face=3D"Calibri" size=3D"3">UNIVERSITY OF CAPE TOWN </font> </p> <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> =20 </p> <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> <font face=3D"Calibri" size=3D"3">This e-mail is subject to the UCT = ICT=20 policies and e-mail disclaimer published on our website at=20 http://www.uct.ac.za/about/policies/emaildisclaimer/ or obtainable = from=20 +27 21 650 4500. This e-mail is intended only for the person(s) to = whom=20 it is addressed. If the e-mail has reached you in error, please = notify=20 the author. If you are not the intended recipient of the e-mail you = may=20 not use, disclose, copy, redirect or print the content. If this = e-mail=20 is not related to the business of UCT it is sent by the sender in = the=20 sender's individual capacity.</font> </p> <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> =20 </p> <p class=3D"msonormal" style=3D"margin-left: 0cm; margin-right: 0cm; = margin-bottom: 10pt; margin-top: 0cm"> <font face=3D"Calibri" size=3D"3">___________________________________= __________________________________________________________________=20 </font> </p> <!--EndFragment--> </BODY></HTML> --=__Part3C16DB77.0__=--