Subcortical neural circuits for ocular accommodation and vergence in primates

Our current knowledge of the neural bases of vergence and accommodation has increased significantly over the past few years. The behavior of medial rectus motoneurons during vergence, which has been reported by a number of investigators, is described. The behavior of Edinger-Westphal neurons during accommodation is also described, as are the characteristics of midbrain near-response neurons in the supraoculomotor area. Evidence that some of these near-response neurons provide the vergence input to medial rectus motoneurons and possibly the accommodation input to Edinger-Westphal neurons is reviewed. Anatomical studies have shown that the midbrain near-response region receives input from two deep cerebellar nuclei, the posterior interposed and the fastigial nucleus. Single-unit recording in the posterior interposed nucleus has revealed cells that increase their activity during the far-response, and the behavior of these neurons is reviewed. In addition, studies of a precerebellar nucleus, the nucleus reticularis tegmenti pontis, have revealed some cells that increase their activity during the near-response and others that do so during the far-response. The behavior of these neurons is reviewed. This review documents the great strides that are occurring in our understanding of the anatomy and physiology of the neural pathways controlling vergence and accommodation in the primate.