Abstract
Computations of acoustic information along the central auditory pathways start in the cochlear nucleus. Bushy cells in the anteroventral cochlear nucleus, which innervate monaural and binaural stations in the superior olivary complex, process and transfer temporal cues relevant for sound localization. These cells are categorized into two groups: spherical and globular bushy cells (SBCs/GBCs). Spontaneous rates of GBCs innervated by multiple auditory nerve (AN) fibers are generally lower than those of SBCs that receive a small number of large AN synapses. In response to low-frequency tonal stimulation, both types of bushy cells show improved phase-locking and entrainment compared to AN fibers. When driven by high-frequency tones, GBCs show primary-like-with-notch or onset-L peristimulus time histograms and relatively irregular spiking. However, previous in vivo physiological studies of bushy cells also found considerable unit-to-unit variability in these response patterns. Here we present a population of models that can simulate the observed variation in GBCs. We used a simple coincidence detection model with an adaptive threshold and systematically varied its six parameters. Out of 567000 parameter combinations tested, 7520 primary-like-with-notch models and 4094 onset-L models were selected that satisfied a set of physiological criteria for a GBC unit. Analyses of the model parameters and output measures revealed that the parameters of the accepted model population are weakly correlated with each other to retain major GBC properties, and that the output spiking patterns of the model are affected by a combination of multiple parameters. Simulations of frequency-dependent temporal properties of the model GBCs showed a reasonable fit to empirical data, supporting the validity of our population modeling. The computational simplicity and efficiency of the model structure makes our approach suitable for future large-scale simulations of binaural information processing that may involve thousands of GBC units.
Highlights
Processing of acoustic information along the auditory pathways is performed in a parallel and hierarchical manner
We focus on globular bushy cells (GBCs), in which the convergence of multiple auditory nerve (AN) inputs substantially contributes to the improvement of phase-locking and entrainment [30,31,32,33,34]
AN inputs to the GBC model were simulated with the established auditory periphery model by Zilany, Bruce and others [58,59,60,61]
Summary
Processing of acoustic information along the auditory pathways is performed in a parallel and hierarchical manner. SBCs send excitatory projections to the ipsilateral medial and lateral superior olive (MSO/LSO) as well as the contralateral MSO [14,15,16], which are the major brainstem structures responsible for binaural sound localization [3]. GBCs innervate several monaural and binaural nuclei in the superior olivary complex [16,17,18,19], including the ipsilateral lateral nucleus of the trapezoid body (LNTB) and the contralateral medial nucleus of the trapezoid body (MNTB), which provide inhibitory projections to MSO and LSO. When stimulated with high-frequency tones (>3 kHz), SBCs show "primary-like (PL)" peristimulus time histograms (PSTHs) that resemble those of AN fibers [15,20], and GBCs usually present "primary-like-with-notch (PLN)" PSTHs having a short pause (~1 ms) of spiking after pronounced onset activity (Fig 1A) [12,19,21,22,23,24]. Enhancement of temporal properties, might be caused through different biophysical mechanisms between SBCs and GBCs [29]
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