Pure tone evoked response audiometry in guinea pigs

This work deals with investigating the pure tone thresholds of unanesthetized guinea pigs by means of the averaged evoked response. Two types of evoked response were seen - the large, rapidly habituating myogenic response i.e. Preyer Reflex Evoked Response (PRER) and the smaller, slowly habituating neurogenic response i.e. Evoked Cortical Response (ECR). The two evoked responses were shown to be different. Only the ECR (mean latency 37 msec) was used in evoked response audiometry. Audiograms were drawn up for each animal and a composite audiogram determined. The composite audiogram compares favorably with the audiograms drawn by the behavioral investigators. Pure tone threshold boundaries were calculated based on those animals whose cochleograms were normal. Using kanamycin and streptomycin, the receptor responsible for the ECR was found to be the cochlea. The vestibular system seemed to play no observable role