Eighth nerve contributions to cat auditory brainstem responses (ABR)

There is a temporal correspondence between some of the early components of the auditory brainstem potentials in cat and the negative peak of the triphasic nerve action potential recorded from selected points along the VIII cranial nerve. The intracranial portion of the VIII nerve in cat has a conduction velocity of 10 meters/s. The initial peak of the ABR, P1a, is coincident with the negative portion of the triphasic VIII nerve action potential within the cochlea as recorded from the round window. The next peak (P1b) of the ABR occurs 400 microseconds later and is coincident with the negative portion of the triphasic VIII nerve action potential recorded from just within the lateral border of the cochlear nucleus. These results are similar to studies of the human ABR that show waves I and II are correlated with activity of the VIII nerve. It is likely that waves P1a and P1b in cat are homologous to waves I and II in human. In cat, these first two peaks of the ABR can be distinguished in vertex to neck recordings but not in vertex to ipsilateral mastoid derivations.