On the Role of the Wideband Inhibitor in the Dorsal Cochlear Nucleus: A Computational Modeling Study

Principal cells (type IV units) in the dorsal cochlear nucleus (DCN) are uniquely sensitive to (are inhibited by) energy minima or notches in acoustic spectra, which provide cues to sound localization. The once accepted conceptual model of the DCN suggested that this sensitivity was shaped largely by inhibitory inputs from wideband inhibitors (WBIs), which received auditory nerve inputs over a wide frequency range and inhibited type IV units over a narrow frequency range. A computational model based on this wide-input narrow-output conceptual model was able to reproduce quantitatively type IV unit responses to notch-noise stimuli as a function of notch width. Recent physiological results have shown however that WBIs are unresponsive to notch-noise stimuli with wide notch widths and thus have narrower auditory nerve fiber input bandwidths than previously assumed. A computational model based on a narrow-input narrow-output model of the WBI was unable to account fully for the notch sensitivity of type IV units suggesting the need to add a new component to the DCN circuit. The goal of this study was to test whether making the output bandwidth of the WBIs wide while keeping their input bandwidth narrow could explain the responses of type IV units to notch-noise stimuli. Anatomical evidence supports this model configuration, and the results show that such a model can produce strong inhibition in type IV units for wide notches. The results thus suggest that WBIs, in narrow-input wide-output form, are sufficient to account for the notch sensitivity of DCN type IV units.