Each year amazed by the incredible carving work of Purdue Audiology student Isabella Huddleston 🤩🤩 via x.com/HeinzLab_Pur... #Halloween 🎃👻

We did some simulations based on this idea, leading to some control on the traveling wave peak (below: variable viscous load). But this mechanism alone could not explain the whole range of amplification/compression that we see in experimental data.

We hypothesized that this ‘gradient’ of velocity could control deformations in the tectorial membrane, modulating viscoelastic loss and giving rise to a mechanism of undamping.

Our proposal stems from recent observation that the three rows of outer hair cells don’t move with the same magnitude. The outer rows show greater motion compared to the most inner row.

In his book on cochlear mechanics, H. Duifhuis uses this comparison to explain the problem of impedance matching at the end of the cochlea (the helicotrema). Likewise, to prevent reflections at the end of a coax cable, it must be terminated with a specific resistance (typically 50 or 75 ohms).

This week I got very excited by the comparison of the cochlea and... a coaxial cable. Both can be well described by a transmission-line model (infinitesimal inductors and shunt impedances put in series).

Ghent, Belgium this morning 🌨️❄️

Henri's work has been to demonstrate that by including a critical oscillator in a traveling-wave model (with some additional features such as 2D hydrodynamic effects or longitudinal coupling), many of the challenges of the Hopf bifurcation approach can be overcome.

But this approach meets some challenges. You maybe noticed it on the previous plot: the bandwidth of the critical-osc model increases too rapidly with level (here in left panel; right panel: gain-bandwidth product).

Another features are related to the compression seen at one location on the cochlea: the sensitivity follows approx. a -2/3 power law, as predicted by a model with critical oscillators (blue: data, black: model). Note that the frequency response also changes with level (the bandwidth increases).

I went to see an exciting PhD defense this week in Paris by H. Ver Hulst under the supervision of Pascal Martin (Institut Curie). His thesis work was on combining critical oscillator models and traveling-wave models for the active cochlea. I'll explain shortly what it's about.