The human auditory brain stem: a comparative view

This study compares human brain stem auditory centers with those of the cat in terms of their topography and cytoarchitecture. Graphic reconstructions of the brain stem pathway illustrate differences in configuration of human auditory centers, such as mediolateral elongation of the cochlear nuclei and rostral prolongation of the superior olivary complex. Greater human brain stem size creates a considerably longer auditory pathway: the distance traversed by axons passing from the cochlear nuclei to the ipsilateral inferior colliculus is approximately 14 mm in the cat and 35 mm in man, while the distance to the contralateral colliculus is about 22 mm in the cat and 46 mm in man. Neuronal groups which are well developed in the human brain stem are the populations of large relay neurons in the cochlear nuclei, the medial olivary nucleus, periolivary region, dorsal nucleus of the lateral lemniscus, and inferior colliculus. In contrast, a number of nuclei and cell groups are very poorly developed or absent in the human auditory system: these include several types of small neurons in the cochlear nuclei, the lateral olivary nucleus, nucleus of the trapezoid body, and ventral nucleus of the lateral lemniscus. The functional implications of these changes are discussed.