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

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.

Midbrain connections of the olivary pretectal nucleus in the marmoset (Callithrix jacchus): implications for the pupil light reflex pathway.

Midbrain projections of the pretectal olivary nucleus (PON) were studied in the marmoset, a New World primate. The fluorescent retrograde tracers Fluoro-Gold (FG) and Fast Blue (FB) were injected into the Edinger-Westphal (EW) nucleus and the lateral terminal nucleus (LTN), respectively. EW nucleus injections resulted in retrograde labeling of significant numbers of FG-positive neurons of the PON as well as a small number of cells in the LTN.