Comparing frequency-chirp sensitivity in the inferior colliculus to basic response properties using novel stimuli

Abstract

Most neurons in the central nucleus of the inferior colliculus (ICC) are sensitive to the direction of phase-curvature of Schroeder-phase (SCHR) stimuli. This phase-curvature controls the direction and velocity of frequency chirps within the fundamental SCHR period. Differences in responses to different SCHR stimuli may originate from an underlying sensitivity to frequency chirp direction or velocity. However, known ICC sensitivities, such as those to frequency or envelope periodicity and duty cycle, may also contribute to the observed effect. To parse these confounding SCHR stimulus features, we designed novel frequency-chirping stimuli to isolate the influences of periodicity, duty cycle, and frequency-chirp direction or velocity on ICC neuron responses. Extracellular, single-unit recordings of chirp responses were made in awake rabbit ICC. Simultaneously, basic response properties were characterized using methods such as frequency response maps, modulation transfer functions, and spectro-temporal receptive fields. By comparing basic response properties across chirp-sensitive neurons (comprising 80% of ICC neurons), we can outline the shared characteristics among them. Our goal is to determine whether frequency-chirp sensitivity in ICC neurons is independent of other established feature sensitivities. Frequency-chirp-sensitive neurons are interesting, because they may play a unique role in encoding sounds with complex phase, including speech. [Work supported by NIDCD-R01-001641.]