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The representation of frequency was mapped in the primary auditory cortex (AI) of C57BL/6J (C57) mice during young adulthood (1.5–2 months) when hearing is optimal, and at 3, 6, and 12 months of age, a period during which progressive, high frequency, sensorineural hearing loss occurs in this strain. Maps were also obtained from CBA/CaJ mice which retain good hearing as they age.

In AI of young adult C57 mice, and CBA mice, characteristic frequencies (CFs) of multiple‐unit clusters were easily identified with extracellular recordings, and a general tonotopic organization was observed from dorsal (high frequency) to ventral and caudal (low frequency). In individual cases there appeared to be deviations from the above tonotopic organization, despite the fact that inbred mice are genetically invariant. As progressive loss of high frequency sensitivity ensued peripherally, a substantially increased representation …