ABR interpeak latencies in rats are shorter at low click intensities

There are conflicting findings concerning whether auditory nerve-brainstem evoked response (ABR) interpeak latencies (e.g. brainstem transmission time - BTT) are constant in response to different stimulus intensities. In order to study the effects of click intensity on the BTT, and to try to determine the mechanism of such an effect, ABR was recorded from 10 adult white Sabra rats in response to different click intensities. The stimulus intensity was reduced from the highest intensity generated by the equipment until no responses could be obtained. Band-reject (notched) noise was presented simultaneously with the clicks in order to restrict the region of basilar membrane activation. BTT decreased with decreasing click intensity and this was accompanied by a prolongation of the latency of wave I to a greater extent than that of wave IV. At high and intermediate intensities, wave I appeared as two split peaks. These effects were not abolished by the restricting notched noise. Possible mechanisms of these latency changes are considered.