Auditory Evoked Potentials in Cats with Neonatal High Frequency Hearing Loss: Evidence of Abnormal Frequency Representation in the Midbrain

Abstract

We have recorded auditory evoked potentials, of both neurogenic and myogenic origin, in cats having neonatal high frequency cochlear hearing loss. Using frequency specific stimuli (tone pips) and by measuring responses near to threshold, we have probed tonotopic (or cochleotopic) representation within the brainstem-midbrain auditory pathway. At stimulus frequencies corresponding to the high frequency cut-off of the cats' audiograms we have observed enhanced amplitudes of both auditory brainstem evoked responses (ABR) and postauricular myogenic (PAM) potentials. We interpret our findings as evidence of a larger than normal population of neurons tuned to this frequency region. We suggest that such abnormal frequency representation results from a long-term sensory deficit caused by lesions to the basal, high frequency region of the cochleas.