title: Effects of excitatory and non-excitatory suppressor tones on two-tone rate suppression in auditory nerve fibers.
abstract: Recordings were obtained from individual auditory nerve fibers in anesthetized chinchillas. Rate versus level functions were obtained for best frequency (BF) tones alone and for simultaneously-gated tone pairs comprising a BF tone and a second tone at a fixed intensity that produced evidence of two-tone rate suppression. Care was taken in selecting a range of suppressor tone levels that included excitatory (i.e., the suppressor tone evoked a rate change by itself) and non-excitatory (i.e., no suppressor tone-evoked rate increase) suppressor tone levels. Addition of a suppressor tone produced a shift of the dynamic range portion of the BF rate versus level function to higher test intensities. A parallel shift of the dynamic range portion of the rate versus level function was associated with a non-excitatory suppressor tone. The shift produced by an excitatory suppressor tone was characterized by a decrease in slope. Results indicated that the magnitude of shift increased monotonically as suppressor tone intensity was raised and that there was a gradual transition from a non-excitatory response to an excitatory response. The rate of shift (i.e., dB of shift per dB change in suppressor tone intensity) did not differ for non-excitatory versus excitatory responses, but was substantially greater for below-BF suppressor tones (1.38 dB/dB) than for above-BF suppressor tones (0.54 dB/dB). The rate of shift did not, however, appear to be related systematically to suppressor tone frequency separation from BF. Above- and below-BF suppression was noted for fibers over the range of best frequencies tested (110 Hz to 16.4 kHz).
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics; D000818:Animals; D002682:Chinchilla; D005072:Evoked Potentials, Auditory; D000159:Vestibulocochlear Nerve / Q000502:physiology*