Relative stereociliary motion in a hair bundle opposes amplification at distortion frequencies

TL;DR

This study reveals that at distortion frequencies, hair bundles exhibit relative stereociliary motions that dissipate energy, preventing amplification of distortion signals and thus potentially improving auditory signal fidelity.

Contribution

The paper demonstrates that relative stereociliary motions at distortion frequencies are dissipative, opposing amplification and suggesting a natural mechanism for reducing auditory distortion.

Findings

Relative stereociliary motions oppose amplification at distortion frequencies.

Tip links engage these relative modes, increasing dissipation.

Hair bundles break into dissipative arrangements at distortion frequencies.

Abstract

Direct gating of mechanoelectrical-transduction channels by mechanical force is a basic feature of hair cells that assures fast transduction and underpins the mechanical amplification of acoustic inputs. But the associated nonlinearity - the gating compliance - inevitably distorts signals. Because reducing distortion would make the ear a better detector, we sought mechanisms with that effect. Mimicking in vivo stimulation, we used stiff probes to displace individual hair bundles at physiological amplitudes and measured the coherence and phase of the relative stereociliary motions with a dual-beam differential interferometer. Although stereocilia moved coherently and in phase at the stimulus frequencies, large phase lags at the frequencies of the internally generated distortion products indicated dissipative relative motions. Tip links engaged these relative modes and decreased the coherence in both stimulated and free hair bundles. These results show that a hair bundle breaks into a highly dissipative serial arrangement of stereocilia at distortion frequencies, precluding their amplification.