Oscillatory flow in the cochlea visualized by a magnetic resonance imaging technique.

We report a magnetic resonance imaging technique that directly measures motion of cochlear fluids. It uses oscillating magnetic field gradients phase-locked to an external stimulus to selectively visualize and quantify oscillatory fluid motion. It is not invasive, and it does not require optical line-of-sight access to the inner ear. It permits the detection of displacements far smaller than the spatial resolution. The method is demonstrated on a phantom and on living rats. It is projected to have applications for auditory research, for the visualization of vocal tract dynamics during speech and singing, and for determination of the spatial distribution of mechanical relaxations in materials.

Mechanical response of frog saccular hair bundles to the aminoglycoside block of mechanoelectrical transduction.

1. Deflections of the mechanosensory hair bundles on frog saccular hair cells were measured interferometrically, with submillisecond temporal and submicrometer spatial resolution, and with subnanometer displacement sensitivity. 2. The direction of the initial bundle deflection (toward the taller stereocilia) in response to a sudden application of aminoglycoside antibiotics shows that the mechanosensory channels are blocked in their mechanically open state. 3. The magnitude of the initial deflection is consistent with published data on the gating swing as derived from the gating compliance. 4. A delayed relaxation and frequently a reversal of the initial deflection were observed and are attributed to the previously reported mechanical adaptation mechanism, which is at least partially controlled by the influx of Ca2+ through the transduction channels. 5. Increases of low-frequency spontaneous motion were found at intermediate blocker concentrations. They can be well accounted for by the fluctuating force exerted on the bundle by the random binding and unbinding of blocker molecules. 6. The mechanical response of the hair bundle to aminoglycosides may be related to their acute and specific ototoxicity.