Phase slips in oscillatory hair bundles

Area of Science:

• Auditory neuroscience
• Mechanobiology
• Nonlinear dynamics

Background:

• Inner ear hair cells possess an active amplification mechanism crucial for sensitive auditory and vestibular signal detection.
• Spontaneous oscillations are observed in isolated hair bundles, indicating inherent active processes within these sensory cells.

Purpose of the Study:

• To investigate the phase-locking dynamics of oscillatory hair bundles under low-amplitude sinusoidal stimulation.
• To characterize the transition to phase-locked states and the associated phenomenon of phase slips.

Main Methods:

• In vitro preparations of auditory and vestibular organs were used to study fluid-immersed hair bundles.
• Phase-locking dynamics were measured by exposing oscillatory bundles to controlled sinusoidal signals.
• The observed transition was analyzed using concepts from nonlinear dynamics, specifically a saddle-node bifurcation on an invariant circle.

Main Results:

• A transition in phase-locking dynamics was observed, characterized by phase slips.
• The rate of phase slips was found to be dependent on the amplitude and detuning of the applied external drive.
• The resulting staircase-like phase structure was accurately reproduced by the stochastic Adler equation, validating its applicability.

Conclusions:

• The study elucidates the nonlinear dynamics governing hair bundle oscillations and their response to external stimuli.
• Phase slip phenomena, predictable by the Adler equation, are key to understanding the transition to phase-locked states in hair cells.
• These findings provide insights into the biophysical mechanisms underlying the exquisite sensitivity of the auditory and vestibular systems.