The vertebrate ear as an exquisite seismic sensor

The neotropical frog Leptodactylus albilabris exhibits the greatest sensitivity to substrate-borne vibrations (seismic stimuli) reported to date for any terrestrial animal. Nerve fibers from the source of this extraordinary sensitivity in the ear show clear stimulus-evoked modulations of their resting discharge rates in response to sinusoidal seismic stimuli with peak accelerations less than 0.001 cm/s2 (10(-6) g). Evidence indicates that its source is the saccule, an organ of hearing in fish and of balance in man. We report that single vibration-sensitive fibers in the white-lipped frog saturate at (whole animal) displacements of 10 A peak to peak [Fig. 1(b)]. Assuming a conservative 20-dB dynamic range for these fibers, the in vivo frog saccule and the mammalian cochlea exhibit roughly equal sensitivities to displacement.