| The cochlear nucleus is the sole target of the auditory nerve fibers. The dorsal part (DCN) is involved in sound localization in the median and parasagittal planes, where interaural sound level and time differences (ILD and ITD) are absent or weak. This functional role is realized by the sensitivity of fusiform cells to the width and frequency of spectral notches that vary according to different sound source elevations.;Notch noise (NN) responses of the principal cell were simulated and compared to the unit with type III response map (RM) responses in the gerbil using a DCN model, which has four groups of neurons: the P-cells representing the principal cells, the 12-cells, representing the narrowband interneuron inhibitors, the W-cells representing the wideband inhibitors, and the AN representing the auditory nerve fibers. This is an extension to the work of Hancock and Voigt 1999, where they simulated type IV unit responses in the cat to NNs. The results showed that fusiform cells are DCN spectral notch detectors.;The tonal responses of P-cells were studied as well by RMs. In this study, 4 of the 5 major unit RM types were successfully simulated with the same model architecture.;In addition to the auditory input, the DCN receives multisensory information via parallel fibers from a variety of sources, including cochlea, cuneate, superior olives, inferior colliculus, auditory cortex, dorsal column nuclei, saccule, and vestibular nerve root. Parallel fibers in the DCN's superficial layer are granule cell axons which innervate DCN's projection neurons, fusiform and giant cells, as well as interneuron inhibitors, cartwheel cells. They are orthogonal to the DCN's isofrequency sheets. Cartwheel cells resemble cerebellum Purkinje cells in morphology, genetics, circuit structure, electro-physiology, and neurochemistry, and fire both single and complex action potentials as well.;The pinna movements may be involved in the sound localization, which could not be modeled by the original DCN model. The parallel fiber system was added to the DCN model: parallel fibers were modeled as current inputs and cartwheel cells were modeled by MacGregor two-point neuromime. Its effects on unit RMs were studied. Three pinna positions were modeled as three different parallel fiber current inputs. The results indicated one of the possible roles of the parallel fiber system in facilitating sound localization: it modifies the units' RMs and also enhances the sensitivity to tones of the chosen units. |
