Hair cell polarity underscores differential responses to efferent neuron suppression. (A) Schematic of the zebrafish lateral line system. Neuromasts (red) containing mechanosensory hair cells send afferent projections (orange) to sensory areas and also receive cholinergic efferent innervation (blue). (B) Efferent fibers transmit a highly-similar, suppressive efference copy signal to all hair cells, regardless of polarity. (C) Glutamatergic output is suppressed in approximately half of hair cells polarized to anterior deflections (green). (D) Glutamatergic output is suppressed in all hair cells polarized to posterior deflections (magenta).