| The dorsal cochlear nucleus (DCN) is part of the ascending auditory pathway and is comprised of an assortment of neuron types arranged into three parallel layers. Its complex neural circuitry is thought to extract spectral cues from acoustic signals under the influence of relevant non-auditory inputs (Young et al. 1995). Fusiform cells and giant cells are the projection neurons of the DCN, sending axons primarily to the contralateral inferior colliculus. Experimental and theoretical methods were used to study different aspects of these projection cells.; Intracellular recording techniques were used to label fusiform cells in barbiturate-anesthetized Mongolian gerbils. The results qualitatively confirm earlier studies showing that fusiform cells exhibit a variety of response properties, including pauser, buildup and chopper, depending on acoustic stimulus parameters (Rhode et al. 1983) and current clamp conditions (Manis 1990). Over the range of best frequencies (0.77–9.85 kHz) exhibited, the tonotopic arrangement quantitatively matches the place-frequency map for the gerbil cochlea, suggesting that the gerbil DCN lacks the high frequency specialization described in the cat (Spirou et al. 1993). The basal dendrites of gerbil fusiform cells are electrotonically more compact than those of the cat (Blackstad et al. 1984). This may partially account for the difference in type IV unit incidence between the two species (Davis et al. 1996; Ding et al. 1999).; Certain physiological characteristics were found to have specific anatomical correlates. Spontaneous rate was related to the basal dendrite arrangement, input resistance was highly correlated with apical dendrite total length, and the transient discharge pattern was correlated with fusiform cell orientation. The structural similarity of the DCN to the cerebellum is used to discuss the general implications of these findings.; Two theoretical studies were undertaken. First, analysis of a lumped parameter circuit model suggested that electrode impalement uniformly increases spontaneous activity across the DCN population, from which it was concluded that cell-to-cell rate comparisons are valid. Second, wideband inhibition was added to a computational model of DCN circuitry to study its role in shaping responses to broadband stimuli. The model simulated responses of DCN projection cells to notch noise with quantitative accuracy. |
