| This thesis investigates various temporal response properties of single neurons in the inferior colliculus (IC) of the anesthetized Mongolian gerbil. Responses to contralateral sinusoidally amplitude-modulated tones were characterized in detail, as stimulus parameters were varied. In response to amplitude-modulation, most neurons showed systematic increases (enhancement) or decreases (suppression) of spike-rate in a manner dependent on modulation-frequency. Most response patterns could be described as some combination of a primary modulation-frequency range of enhancement, a higher modulation-frequency range of suppression, and occasionally, a secondary region of enhancement at even higher modulation-frequencies, with each region present to varying degrees in individual neurons. The region of suppression tended to occur in neurons with sustained or pauser responses to pure-tones, usually emerged at higher sound-pressure levels (SPLs), and was not the result of sideband inhibition. The lowest modulation-frequency producing a clear peak in the response (BMF) usually lay between 0 and 100 Hz, and often varied substantially with SPL. In comparison to the cochlear nucleus, synchronization of IC neurons showed higher peak-values, but lower upper modulation-frequency limits. Responses also showed larger phase-advances at a given modulation-frequency as SPL was increased; the magnitude of phase-advance depended upon modulation-frequency. Most IC neurons also showed a simple non-decreasing total response as tone-duration was increased. The lowest tone duration (threshold duration) that evoked a reliable response mostly lay between 1 and 100 milliseconds. Also, mean and standard-deviation of first-spike latency were measured as pure-tone SPL and rise-time were varied. About half the neurons showed a systematic decrease of latency with increases in SPL and decreases in rise-time; most other neurons showed increases of latency with increases in SPL. The decreasing behavior was similar to reported responses from auditory nerve and cortex; a minimal model of the auditory nerve that reproduces almost all the physiological data from the auditory nerve population is described in an Appendix. Temporal response properties measured in these different experiments were strongly correlated: IC neurons with higher BMFs tended to show higher firing-rates at BMF, lower minimum latencies, and lower threshold durations. The results provide useful constraints for physiological models of auditory temporal processing. |
