Brainstem, whole-nerve AP and single-fiber suppression in the gerbil: normative data.

Suppression of gerbil brainstem responses (BSRs) and whole-nerve AP responses was studied by means of a forward masking procedure in which a tone-burst probe was preceded by a narrow-band masker. The effectiveness of the masker in reducing the brainstem response to the probe can be diminished by presenting a tone burst simultaneously with the masker. By varying the frequency and intensity of the third stimulus, BSR suppression areas can be determined. These flank the tails and high-frequency sides of BSR tuning curves in a manner similar to the suppression areas of AP tuning curves. The shapes and sizes of the BSR and AP suppression areas vary greatly across probe frequencies and animals. However, the lower boundaries of suppression areas associated with the tails of the tuning curves occur at similar absolute levels regardless of probe frequency or tuning curve shape. The BSR and AP suppression areas are in some respects similar to areas of two-tone rate suppression in single auditory nerve fibers of the gerbil.