Projects

PhD thesis : Sampling, visualization and analysis of vibration data

For my PhD research project in the area of auditory mechanics I discovered the physics behind frequency discrimination in the katydid ear. It turns out that katydids use the same mechanism as humans to discriminate frequencies, called traveling waves. An example of a traveling wave can be seen in Video 1. Video 2 demonstrates how traveling waves are propagated by reflection. Video 3 shows how the transducers are displaced by the traveling wave.

Vibration data were collected during sound stimulation using a laser Doppler vibrometer. A Fourier analysis was done at the stimulus frequency. The videos are animations of phase reconstructions of vibration magnitude superimposed on the microscope image at the stimulus frequency. The data was sampled at several points non-uniformly on the hearing organ and interpolated to create a continuous surface. For more explanation of the method : download PhD thesis

Video 1: A traveling wave elicited in the katydid hearing organ at 12 kHz. The vibration data was collected using a laser Doppler vibrometer at various points on the hearing organ, interpolated and animated to visualize the wave.

Video 2: Using ISO lines representing vibration velocity, the video above shows how traveling waves are reflected off the walls of the acoustics trachea in a katydid hearing organ.

Video 3: The video above demonstrates place based frequency discrimination or tonotopy. Here you can see how a frequency of 12 kHz elicits a peak in vibration velocity towards the proximal part of the hearing organ displacing the tiny receptors (circle shaped) that transduce mechanical vibration to electrical signals.

Masters thesis: Numerical solution of partial differential equations

The mechanical properties of the tectorial membrane (TM) are known to be crucial for normal function of the cochlear amplifier. Being a polyelectrolyte gel, the chemical, mechanical, electrical and osmotic properties of the TM have been shown to be inextricably linked. It has also been proposed that the TM might act as an ionic buffer. Since mechanoelectrical transduction (MET) in the hair-cell stereocilia is strongly dependent on [Ca²⁺], it is not inconceivable that the TM might act as a [Ca²⁺] buffer. Therefore, here, we present a model of [Ca²⁺] dynamics in the subtectorial space which highlights the possible role of the TM as a regulator of extracellular [Ca²⁺] in the region of the stereocilia.

For [Ca²⁺] dynamics in the stereocilium, the one-dimensional diffusion model introduced by Lumpkin and Hudspeth (1998) was modified to represent the stereocilium of an outer hair cell. Extracellular [Ca²⁺] dynamics in the surrounding subtectorial space was simulated in three dimensions using Fickís law of diffusion in a cylindrical coordinate system. A calcium buffer was placed at the lower surface of the TM, adjacent to the subtectorial space. Local [Ca²⁺] transients were produced in this extracellular space by modulation of the open probability of the MET channel in the stereocilium. Using buffer concentrations and rate constants for the stereocilium similar to those in the LH-model and an ambient extracellular [Ca²⁺] of 30 µM, the extracellular transient in the region of the channel can be as much as 7 µM in the absence of a TM buffer, but an order of magnitude smaller in the presence of the buffer. We found an inverse relation between the dissociation constant of the TM buffer and its concentration that yielded an ambient [Ca²⁺] of 30 µM.

In conclusion, we show that during transduction a TM calcium buffer, together with a stable [Ca²⁺] within the TM, can maintain the [Ca²⁺] in the extracellular fluid near its ambient level. download thesis.

Masters level :

Lab rotations

Gummer Lab, THRC, Tuebingen, Germany-->

The first lab rotation was a purely analytical project in cochlear fluid mechanics. The project investigated that effect and existence of slip between the endolymph and the tectorial membrane. It was supervised by Prof. Anthony. W. Gummer. It was found that the slip was very small and that it did not significantly alter fluid motion. The project was completed in three months time. download report

De Schutter lab, University of Antwerp, Belgium -->

Under the supervision of Dr.Pablo Achard, I learnt how to simulate Purkinje cell models on Genesis. I am currently working on Calcium dynamics in the Purkinje cell. The model captures calcium buffering, calcium pumps and one dimensional radial diffusion of calcium. This work is a continuation of the interesting results published by Dr.Achard and Dr.De Schutter in PLoS computational Biology where tight constraints were found on the variation of calcium conductance.