UC Irvine

Single unit activities in the region of the superior olivary complex were recorded from 8 guinea pigs concurrently with the recording of auditory brainstem potentials from the scalp. At any one anatomical site, be it a fiber tract (e.g. trapezoid body) or a nucleus (e.g. medial nucleus of the trapezoid body), the modal latency of the onset discharge of the units encountered corresponded in time with the latencies of several different waves (waves P2-P5) of the auditory brainstem response (ABR). Moreover, at the time of occurrence of just one of the ABR waves, single units in several diverse anatomical sites in and around the superior olive were found with modal latencies of onset discharge at that same time period. The slopes of the latency/intensity functions for both the peaks of the ABR and the modal latency of the onset discharge for most of the single units studied in the superior olive and its adjacent fiber tracts were remarkably similar. These data support the hypothesis of multiple rather than single generator site(s) for components of the ABR, at least, for waves P2-P5 in the guinea pig. These data do not distinguish whether the ABR are generated in part by travelling nerve action potentials or graded synaptic events.