A physiological place-frequency map of the cochlea in the CBA/J mouse

Abstract

Genetically manipulated mice have gained a prominent role in in vivo research on development and function of the auditory system. A prerequisite for the interpretation of normal and abnormal structural and functional features of the inner ear is the exact knowledge of the cochlear place-frequency map. Using a stereotaxic approach to the projection site of the auditory nerve fibers in the cochlear nucleus, we succeeded in labelling physiologically characterized auditory nerve afferents and determined their peripheral innervation site in the cochlea. From the neuronal characteristic frequency (CF) and the innervation site in the organ of Corti a place-frequency map was established for characteristic frequencies between 7.2 and 61.8 kHz, corresponding to locations between 90% and 10% basilar membrane length (base = 0%, apex = 100%, mean length measured under the inner hair cells 5.13 mm). The relation between normalized distance from the base (d) and frequency (kHz) can be described by a simple logarithmic function: d(%) = 156.5-82.5 x log(f), with a slope of 1.25 mm/octave of frequency. The present map, recorded under physiological conditions, differs from earlier maps determined with different methods. The simple logarithmic place-frequency relation found in the mouse indicates that mice are acoustic generalists rather than specialists.