Auditory brain stem responses in the cat. I. Intracranial and extracranial recordings.

A spatial and temporal analysis of auditory evoked potentials within the brain stem were performed in cats to determine the areas of the brain stem having large amplitude voltage fields, corresponding in latency to each of the components of the scalp-recorded auditory brain stem response (ABR). On the basis of this criterion, the first few components (occurring within 2 msec post-stimulus) were attributed to activity in a single structure, the eighth nerve. In contrast, each of the other components was correlated with large amplitude fields in at least two sites within the brain stem auditory pathways. The findings demonstrate a complex spatial and temporal distribution of electrical events within the auditory brain stem pathways, which preclude any simple one-to-one relationship between a given anatomical site and a particular component of the ABR. The possibility that the determination of the generators might be influenced by filtering of the evoked potentials was also examined. High-pass filtering of the evoked potentials resulted in a modification of the defined generators for only one of the components studied (P4). Filtering had little effect on the components of the scalp-recorded ABR.