Individual variability in the nuclei of the human superior olivary complex

The superior olivary complex (SOC) receives auditory information from the cochlear nuclei. In nonhuman mammals, the SOC contains three nuclei: the lateral and medial superior olives (LSO, MSO) and the medial nucleus of the trapezoid body (MNTB). There are also periolivary neurons that are assigned to different nuclei in different mammals. The configuration of the SOC in the human differs from that in other species. The LSO is less well-defined; some authors do, and others do not, find an MNTB, and different authors recognize different periolivary nuclei. We have studied the organization of the human SOC using Nissl and immunostained sections of 12 brains from the Witelson Normal Brain Collection. We found an MSO in all cases although it varied in rostro-caudal extent. We did not consistently see a grouping of neurons consistent with an LSO in Nissl sections. Calbindin (CB) is expressed in neurons of the MNTB in several species. We found CB-immunoreactive (ir) cells in all human cases, some in the expected location of the MNTB, however these CB-ir neurons varied in number and location among cases. The variability in SOC configuration suggests there may also be individual variability in sound localization, a major function mediated by the SOC.