An anatomically based frequency-place map for the mouse cochlea

An anatomically based frequency-place map was created for the mouse using C57BL/CBA F1 hybrids by matching noise-induced lesions in the organ of Corti with permanent hearing losses as determined by auditory brainstem response (ABR) thresholds. Twenty-six mice developed 'notched' ABR threshold shifts after exposure to an octave band of noise with a center frequency of 2 kHz at 120 dB SPL for 24 h, 4 kHz at 110 dB SPL for 4 h or 8 kHz at 100 dB SPL for 1 or 2 h. ABR thresholds were determined at several intervals post-exposure until thresholds stabilized (14-27 days). Once thresholds had stabilized, the mice were killed and their cochleas were prepared for phase-contrast microscopic examination as plastic-embedded flat preparations. Hair cell loss, stereocilia damage, and myelinated nerve fiber degeneration as a function of percentage distance from the cochlear apex were determined. Frequency-position matches could be made for 22 of the 26 mice by correlating areas of hair cell loss/stereocilia damage with permanent changes in ABR thresholds. These frequency-position data were fitted with the equation: % Distance from apex=56.6 log (f(Hz))-179.1; r(2)=0.810. This frequency-place function agrees well with Ehret's (1975) theoretical function based on critical bands and masked auditory thresholds.