A network model for the functional architecture of the mammalian medial superior olivary nucleus

Abstract

The mammalian MSO is part of the superior olivary complex, the lowest level in the auditory pathway, which receives binaural input. The microarchitecture of the anatomical convergence of both paths is considered as fundamental for the nucleus’ function in time-domain processing. This architecture is mostly, according to a proposal of Jefress [L. Jefress, J. Comp. Physiol. Psychol., 35–39 (1948)], interpreted as a network of coincidence detectors. However, the topographic organization of the afferent innervation of the MSO shows much more complexity as is assumed in this model. The connection scheme of the afferent fibers indicates even aspects of terminal divergence, which should result in broadly tuned neurons instead of sharply tuned coincidence detectors. This study proposes a network model for the processing of interaural time delays (ITD) in the MSO based on connection patterns and response properties of the MSO fusiform cells. Instead of local coincidence detection, coding of ITD’s is distributed over a cluster of fusiform cells, where each individual cell’s degree of stimulus resolution is considered as low. While in the Jefress model each delay line is processed as a single channel, cluster formation based on MSO’s multipolar cells could be a mechanism for sampling over these different channels.