Spectrotemporal response properties of neurons in the guinea pig dorsal cochlear nucleus to stimulation with periodic wideband noise.

Abstract

Spectrotemporal receptive field (STRF) analysis was used to study neural response properties in guinea pig dorsal cochlear nucleus (DCN) for acoustic stimulation with periodic, wideband noises. The approach estimated the average time-frequency patterns of energy fluctuations in the stimuli associated with neural firing, but without the restrictions of standard reverse-correlation methods (i.e., not limited to phaselocked units). The STRF patterns consisted of high-energy peak regions, and occasionally low energy trough areas, where the frequency associated with the maximum peak was correlated with the unit's best frequency (BF). Two major STRF pattern classes were characteristic of particular unit response types for toneburst stimulation (peristimulus time histogram classification): a single, long-duration peak region was seen for most pauser/buildups; while choppers usually exhibited multiple bands (combinations of peaks, or peaks and troughs), spaced at regular time intervals. These STRF patterns are described in the first of three reports forming the body of this work. The second report focuses on the unique temporal response properties evoked in DCN units by the noise stimulation. Many pauser/buildups and chopper-types exhibiting temporally complex STRF patterns also had discharge periodicities in response to noise stimulation. Two categories of periodicities were observed: the first reflected synchronization to particular phases of individual frequency components in the noise; the second was a lower-frequency periodicity, similar to the "intrinsic oscillations" observed with amplitude-modulated stimuli for the same unit classes. The third study focused on frequency selectivity properties of unit noise responses in the presence of continuous tone maskers. Dependent on masker frequency and intensity, the tonal maskers had variable effects on discharge rate, from complete rate suppression to partial summation, with greatest masking observed for maskers of moderate intensities at BF. Addition of the masker tones also caused a loss of temporal patterning in the period histograms and STRF patterns. The periodic noise stimuli and this spectrotemporal analysis provided information about unit responses to complex signals beyond those available from more traditional methods.