Vestibular neuroanatomy: recent observations.

The modern neuroanatomical technique of using a retrograde axoplasmic tracer (horseradish peroxidase) to label neurons has aided the revelation of several important connections in the vestibular system. The organization of the oculomotor nucleus and the existence of an interneuron in the abducens nucleus have importance in understanding some ocular disorders. A detailed description of the location of vestibulo-ocular neurons to individual extraocular muscles is now available which may provide a basis for understanding how these reflexes function normally and abnormally. Interconnections between the vestibular nuclei are provided by commissural neurons located in the superior, medial and group Y nuclei. These projections are probably of importance in vestibular compensation. A possible hypothesis of vestibular hair cell projection suggests that type I cells project over vestibulo-ocular neurons while type II cells project over commissural pathways.