Neural modeling of the dorsal cochlear nucleus: cross-correlation analysis of short-duration tone-burst responses.

Abstract

A conceptual model of a portion of dorsal cochlear nucleus (DCN) neural circuitry has emerged over the past two decades. This model suggests that the response properties of the DCN's major projection neurons, called type IV units, are due, in part, to the behavior of local circuit inhibitory interneurons called type II units (Young and Brownell 1976). Cross-correlation studies of simultaneously recorded pairs of DCN units in decerebrate cat derived from 50-s best frequency (BF) stimuli are consistent with and have extended this conceptual model (Voigt and Young 1980, 1985, 1988, 1990). Interestingly, Gochin et al. (1989) found no signs of inhibition in the anesthetized rat DCN in cross-correlograms derived from 55-ms short-duration BF tone bursts. This seemingly contradictory result has motivated this study. Computer simulations were run using our network model of the intrinsic DCN neural circuitry. This model has previously been shown to reproduce the major features of both type II and type IV rate-level curves and the inhibitory trough (IT) observed in cross-correlograms derived from long-duration stimuli (Voigt and Davis 1994). The goal was to study the stimulus-duration-dependent strength of ITs in the cross-correlograms derived from short-duration BF tone-burst stimuli. The results suggest that ITs may not be detectable when the stimulus duration is 50 ms but may be detectable when the stimulus duration is 200 ms or greater. Furthermore, when the ITs are detected in cross-correlograms derived from 200-ms data sets, the strength of the IT, as measured by effectiveness, is comparable to the strength of ITs measured when the stimulus duration is 50 s.