Superior olivary nucleus

Superior olivary complex
Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red. (Superior olivary nucleus is labeled at center right.)
Details
Identifiers
Latin	nucleus olivaris superior
NeuroNames	hier-565
NeuroLex ID	Superior olivary complex
Dorlands /Elsevier	n_11/12582125
TA	A14.1.05.415
FMA	72247
Anatomical terms of neuroanatomy []

The superior olivary complex (or SOC or superior olive) is a collection of brainstem nuclei that functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the auditory system. The SOC is intimately related to the trapezoid body: most of the cell groups of the SOC are dorsal (posterior in primates) to this axon bundle while a number of cell groups are embedded in the trapezoid body. Overall, the SOC displays a significant interspecies variation, being largest in bats and rodents and smaller in primates.

The superior olivary nucleus plays a number of roles in hearing. The medial superior olive (MSO) is a specialized nucleus that is believed to measure the time difference of arrival of sounds between the ears (the interaural time difference or ITD). The ITD is a major cue for determining the azimuth of sounds, i.e., localising them on the azimuthal plane – their degree to the left or the right.

The lateral superior olive (LSO) is believed to be involved in measuring the difference in sound intensity between the ears (the interaural level difference or ILD). The ILD is a second major cue in determining the azimuth of high-frequency sounds.

The superior olivary complex is generally located in the pons, but in humans extends from the rostral medulla to the mid-pons and receives projections predominantly from the anteroventral cochlear nucleus via the trapezoid body, although the posteroventral nucleus projects to the SOC via the intermediate acoustic stria. The SOC is the first major site of convergence of auditory information from the left and right ears.

The superior olivary complex is divided into three primary nuclei, the MSO, LSO, and the Medial nucleus of the trapezoid body, and several smaller periolivary nuclei. These three nuclei are the most studied, and therefore best understood. Typically, they are regarded as forming the ascending azimuthal localization pathway.

The medial superior olive is thought to help locate the azimuth of a sound, that is, the angle to the left or right where the sound source is located. Sound elevation cues are not processed in the olivary complex. The fusiform cells of the dorsal cochlear nucleus (DCN), which are thought to contribute to localization in elevation, bypass the SOC and project directly to the inferior colliculus. Only horizontal data is present, but it does come from two different ear sources, which aids in the localizing of sound on the azimuth axis. The way in which the superior olive does this is by measuring the differences in time between two ear signals recording the same stimulus. Traveling around the head takes about 700 μs, and the medial superior olive is able to distinguish time differences much smaller than this. In fact, it is observed that people can detect interaural differences down to 10 μs. The nucleus is tonotopically organized, but the azimuthal receptive field projection is "most likely a complex, nonlinear map".