Pathways connecting the right and left cochlear nuclei.

Connections between the right and left cochlear nuclei were studied with retrograde and anterograde axonal transport techniques. Large, multipolar neurons in the anterior and posterior divisions of the anteroventral cochlear nucleus and in the posteroventral cochlear nucleus project to the ventral and dorsal cochlear nuclei on the opposite side. In addition, giant cells in the deep layers of the dorsal cochlear nucleus project to the contralateral posteroventral cochlear nucleus and possibly also to the contralateral dorsal cochlear nucleus. The pattern of terminal distribution of the crossed connections was determined by using the anterograde axonal transport of horseradish peroxidase-labelled wheat germ lectin. Although no part of the cochlear nuclear complex is completely free of anterograde label, the densest labelling is found in the anterior division of the anteroventral cochlear nucleus, throughout the posteroventral cochlear nucleus (where it is closely associated with cell bodies), and in the fusiform and superficial layers of the dorsal cochlear nucleus. These direct synaptic connections from one cochlear nucleus to the other could play a significant role in processes that depend on binaural interactions within the central nervous system.