The afferent ganglion cells and cortical projections of the retinal recipient zone (RRZ) of the cat's ‘pulvinar complex’

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Abstract
A retino‐pulvinar projection in the cat was confirmed using anterograde (autoradiography) and retrograde (horseradish peroxidase (HRP) tracing techniques. The part of the ‘pulvinar complex’ receiving retinal afferents is referred to as the retinal recipient zone (RRZ). The cortical projections of the RRZ were studied by injecting HRP into different cortical areas. The retrograde labeling of the cell bodies and dendritic fields of the retinal ganglion cells projecting to the RRZ was accomplished by injecting HRP electrophoretically into the RRZ.Our results indicate that the RRZ projects to areas 19 and the lateral suprasylvian area (LS) but not to areas 17 or 18. Virtually all RRZ cells, including those that project to the cortex, are small (10–20 μm in diameter); they are the same size as the relay cells of the parvocellular C laminae of the lateral geniculate nuclear complex (LGNd) that project to areas 19 and LS.The majority of the ganglion cells projecting to the RRZ had medium‐sized somas (15–25 μm in diameter), large (up to 800 μm in diameter), diffuse dendritic fields with a characteristic morphology, and appeared different form the alpha, beta, gamma, and delta cells of Boycott and Wässle (′74). These cells provide evidence for another morphological class of ganglion cells, termed epsilon cells.Our results suggest that the RRZ relays the activity of specific types of retinal ganglion cells to extrastriate visual cortex and, thus, functions in parallel with the different subdivisions of the LGNd.