The accessory optic system: basic organization with an update on connectivity, neurochemistry, and function

Prog Brain Res. 2006;151:407-40. doi: 10.1016/S0079-6123(05)51013-6.


The accessory optic system (AOS) is formed by a series of terminal nuclei receiving direct visual information from the retina via one or more accessory optic tracts. In addition to the retinal input, derived from ganglion cells that characteristically have large receptive fields, are direction-selective, and have a preference for slow moving stimuli, there are now well-characterized afferent connections with a key pretectal nucleus (nucleus of the optic tract) and the ventral lateral geniculate nucleus. The efferent connections of the AOS are robust, targeting brainstem and other structures in support of visual-oculomotor events such as optokinetic nystagmus and visual-vestibular interaction. This chapter reviews the newer experimental findings while including older data concerning the structural and functional organization of the AOS. We then consider the ontogeny and phylogeny of the AOS and include a discussion of similarities and differences in the anatomical organization of the AOS in nonmammalian and mammalian species. This is followed by sections dealing with retinal and cerebral cortical afferents to the AOS nuclei, interneuronal connections of AOS neurons, and the efferents of the AOS nuclei. We conclude with a section on Functional Considerations dealing with the issues of the response properties of AOS neurons, lesion and metabolic studies, and the AOS and spatial cognition.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cerebral Cortex / anatomy & histology
  • Cerebral Cortex / physiology
  • Columbidae
  • Geniculate Bodies / anatomy & histology
  • Geniculate Bodies / physiology
  • Humans
  • Mammals
  • Mesencephalon / anatomy & histology
  • Mesencephalon / physiology
  • Neural Pathways / anatomy & histology
  • Neural Pathways / physiology
  • Neurons / chemistry
  • Neurons / ultrastructure
  • Neurotransmitter Agents / analysis
  • Neurotransmitter Agents / physiology
  • Nystagmus, Optokinetic / physiology
  • Olivary Nucleus / anatomy & histology
  • Olivary Nucleus / physiology
  • Opioid Peptides / analysis
  • Opioid Peptides / physiology
  • Phylogeny
  • Reticular Formation / anatomy & histology
  • Reticular Formation / physiology
  • Retina / anatomy & histology
  • Retina / physiology
  • Spatial Behavior / physiology
  • Species Specificity
  • Vertebrates / anatomy & histology*
  • Vertebrates / physiology
  • Visual Pathways / anatomy & histology*
  • Visual Pathways / chemistry
  • Visual Pathways / physiology


  • Neurotransmitter Agents
  • Opioid Peptides