| 1995, 696, Session T6, Poster |
| Two-tone suppression displayed by auditory-nerve fibers with different spontaneous rates |
| *Y. Cai, C.D. Geisler (University of Wisconsin-Madison, Madison) |
| The responses of 190 auditory-nerve fibers with different spontaneous rates were studied in anesthetized cats, using harmonically related characteristic frequency (CF) tones and suppressor tones (50-2000 Hz) as stimuli.
Period histograms were constructed with respect to the period of the suppressor tone for three stimulus conditions: CF-tone alone, two-tone, and suppressor-tone alone. The vector phase of the response to suppressor tone alone and the phase of suppression were not dependent on the spontaneous rate (SR) of the fiber.
However, the relative response level, defined as the ratio of the maximum response rate occurring during the two-tone stimulus to the response rate during the CF-alone stimulus (at or near the intensity where the rate suppression was greatest) was dependent on fiber SR.
For all the suppressor frequencies used, lower-SR fibers almost always showed a relative response level less than unity, while high-SR fibers generally exhibited levels around or greater than unity.
In one experiment, a pair of low- and high-SR fibers with the same CF (12 KHz) were recorded consecutively in the same electrode penetration, and were studied with the same stimulus parameters.
The temporal nature of responses showed very close resemblances, in that their phases of excitation and suppression were virtually the same. But the amplitude characteristics were quite different, and did not seem to be explained by a simple threshold model at the afferent-fiber synapse.
These results support the hypothesis that the basic temporal excitation and suppression patterns for all auditory-nerve fibers are formed at or before the inner-hair-cell stage, while the discharge rates depend phasically upon the characteristics of the particular synapses involved. Possibly the different dynamics of adaptation which exist between lower- and high-SR fiber synapses are involved. |
| Supported by NIH grant NIDCD-DC00116
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Citation for this abstract:
Cai, Y. and C.D. Geisler (1995). Two-tone suppression from auditory-nerve fibers with different spontaneous rates. Assoc. Res. Otolaryngol. Abstr., p.174.
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