Comparison between the tuning properties of inner hair cells and basilar membrane motion

Measurements were made of inner hair cell receptor potentials and basilar membrane motion in the 17–21 kHz region of the guinea pig cochlea. The latter were made using the Mossbauer technique. Isoamplitude curves at 0.9 mV d.c. receptor potential were compared with isovelocity curves at 0.04 mm/s and the corresponding basilar membrane displacement at CF. The Mossbauer source (20 × 60 or 60 × 85 μm) was placed either in the middle of the basilar membrane or on the extreme modiolar edge. These two source positions yielded broad and narrow mechanical tuning curves, respectively. The latter approximated the receptor potential curves most closely but deviated by 10–15 dB on the low frequency side of the tuning curve tip.