Laminar origin of direct projection from cortex area V1 to V4 in the rhesus monkey.

Direct projection from cortex area V1 to V4 in the rhesus monkey was demonstrated by means of retrograde axonal transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). This projection originated at the layers 2 and 3 of the only representation area of central visual field (0-6 degrees) in V1 and terminated at the central representation of V4, whereas there was no projection between the extracentral representations of V1 and V4. Correlation of the present finding with the previous findings suggests that this projection is predominantly involved in the system of color information processing.