superior olivary complex

The superior olivary complex (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. Physiology 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.