Temporal and Binaural Properties in Dorsal Cochlear Nucleus and Its Output Tract

Abstract

The dorsal cochlear nucleus (DCN) is one of three nuclei at the terminal zone of the auditory nerve. Axons of its projection neurons course via the dorsal acoustic stria (DAS) to the inferior colliculus (IC), where their signals are integrated with inputs from various other sources. The DCN presumably conveys sensitivity to spectral features, and it has been hypothesized that it plays a role in sound localization based on pinna cues. To account for its remarkable spectral properties, a DCN circuit scheme was developed in which three inputs converge onto projection neurons: auditory nerve fibers, inhibitory interneurons, and wide-band inhibitors, which possibly consist of Onset-chopper (O c ) cells. We studied temporal and binaural properties in DCN and DAS and examined whether the temporal properties are consistent with the model circuit.Interneurons (type II) and projection (types III and IV) neurons differed from O c cells by their longer latencies and temporally nonlinear responses to amplitude-modulated tones. They also showed evidence of early inhibition to clicks. All projection neurons examined were inhibited by stimulation of the contralateral ear, particularly by broadband noise, and this inhibition also had short latency. Because O c cells had shortlatency responses and were well driven by broadband stimuli, we propose that they provide short-latency inhibition to DCN for both ipsilateral and contralateral stimuli. These results indicate more complex temporal behavior in DCN than has previously been emphasized, but they are consistent with the recently described nonlinear behavior to spectral manipulations and with the connectivity scheme deduced from such manipulations. Key words: audition; dorsal cochlear nucleus; dorsal acoustic stria; amplitude modulation; temporal; binaural; catThe dorsal cochlear nucleus (DC N) is one of three nuclei at the terminal zone of the auditory nerve. Axons of its projection cells leave the nucleus via the dorsal acoustic stria (DAS) and project to the inferior colliculus (IC) (Osen, 1972;Adams and Warr, 1976;Oliver, 1984). The DC N is the most complex subdivision of the cochlear nucleus, and its f unction remains unknown. Young and colleagues (1992) proposed that the DC N serves a role in the detection of spatial elevation of a sound source by virtue of its sensitivity to spectral features such as those resulting from the directionally dependent filtering properties of the pinna.One strategy for obtaining clues to the f unction of the DCN is to examine the effect of its very nonlinear spectral properties (Nelken et al., 1997) on the IC (Semple and Aitkin, 1980). For example, inputs from the DC N partly converge with inputs from the lateral superior olive (L SO) (Oliver et al., 1997). C ells in the LSO are sensitive to interaural level differences (ILDs) (Boudreau and Tsuchitani, 1968) and interaural time differences of amplitude-modulated (AM) tones , which are cues to the azimuthal position of a sound source. C ells in the IC with spatially restricted receptive fields...

Temporal properties of responses to sound in the ventral nucleus of the lateral lemniscus

“…Sources of inhibition are discussed by Zhang and Kelly (2006a) and include projections from the superior olivary complex as well as intrinsic circuitry. Also, the weak binaural interaction in the VNLL is perhaps inherited from the VCN (Joris and Smith 1998;Recio-Spinoso 2005;Shore et al 2003). Interestingly, the sign of the binaural interaction is dominantly EI (contralateral ear excitatory, ipsilateral ear inhibitory), similar to high-CF neurons in the IC.…”

Limited Segregation of Different Types of Sound Localization Information among Classes of Units in the Inferior Colliculus

“…Sound localization cues are segregated, to some extent, in brainstem nuclei: DCN neurons respond to SNs but not to ITDs and only weakly to ILDs (Young and Brownell, 1976;Joris and Smith, 1998); MSO neurons respond to ITDs but weakly to ILDs (Goldberg and Brown, 1969); and LSO neurons respond strongly to ILDs but weakly to ITDs . Of course, neurons in both MSOs and LSOs should respond to SNs, like any tuned neuron.…”

Auditory Midbrain and Nerve Responses to Sinusoidal Variations in Interaural Correlation

“…Stimuli were generated with a 16 bit, 524 kHz digital stimulus system (Olson et al, 1985). Precautions were taken to minimize acoustic crosstalk through the stimulus system (Gibson, 1982), and control experiments in the auditory nerve (AN) (see below) (Joris and Smith, 1998) confirmed the high level of acoustic isolation.…”