Subcortical structures projecting to visual cortical areas in squirrel monkey.

In 17 adult squirrel monkeys (Saimiri), horseradish peroxidase was used as a retrograde tracer substance to reveal the subcortical structures (other than the lateral geniculate nucleus and pulvinar) which project to the occipital lobe, and, in particular, to the central visual field representation in areas, 17, 18, 19, and MT. Evidence is provided that each of areas 17, 18, and MT receives a projection from locus coeruleus, nucleus dorsalis raphae, nucleus annularis, nucleus centralis superior, formation reticularis pontis oralis, nucleus basalis of Meynert, lateral hypothalamus, claustrum, and nuclei paracentralis and centralis medialis thalami. Area 19 receives a projection from all these structures except from the nucleus annularis. Only area MT was determined to be a target of a projection from the nucleus linearis. For technical reasons, only area MT was determined to receive afferent fibers from the nucleus basalis lateralis amygdalae. The results indicate that there is no topographical organization of subcortical inputs to the central visual field representation in individual cortical areas.