Efferent control of synchronization among coupled hair bundles

Hair cells of the inner ear constitute biological detectors that respond to auditory and vestibular signals. Deflection of the stereocilia triggers the opening of mechano-sensitive transduction channels and enables the influx of ionic currents. This detection process includes active amplification of the signal, which is critical for the required sensitivity of the system. In this study, we apply direct electrical stimulation to efferent neurons in order to explore their impact on hair bundle dynamics. In vivo, hair bundles (HBs) of auditory and vestibular epithelia are coupled to each other via otolithic or tectorial membranes. We therefore explore how actuation of the efferent neurons modulates or shapes the collective response of coupled hair bundles. We achieve artificial coupling of HBs of the sacculi of the American Bullfrog by attaching them to mica flakes. The experimental setup allows optical recording of the HBs’ active motility, while electrically stimulating the auditory nerve in an ex vivo preparation that emulates physiological conditions.