Orientation specificity in the mammalian visual pathway and retinal ganglion cell dendritic morphology.

The aim of the first investigation of this dissertation was to relate the orientation preferences of visual cortical neurons to the orientations of retinal ganglion cell dendritic fields in the cat. The preferred orientations of Simple cells in striate and extrastriate cortex and of Complex cells with narrow receptive fields in striate cortex but not those with wide receptive fields in striate and extrastriate cortex matched the orientations of the topographically corresponding ganglion cell dendritic fields. The columns representing the radial orientation are wider than those representing nonradial. This evidence indicates that the orientation specificity of cortical cells is related to the orientation sensitivity of retinal ganglion cells. The dendritic shape of ganglion cells in the macaque retina was also analyzed. Most of the dendritic fields were elongated, and there was a significant tendency for the dendritic fields to be oriented radially with respect to the fovea. The aim of the third investigation was to relate the variation of two attributes of dendritic morphology to the topography of the retina. The first attribute was the displacement of the center of the dendritic field from the center of the cell body. Ganglion cell dendritic fields tend to be displaced from the soma down the ganglion cell density gradient. The systematic displacement of the dendritic fields results in the dendritic field centers being arranged more regularly than are their cell bodies. The second attribute was the elongation and orientation of ganglion cell dendritic fields. The cat retina undergoes a process of maturation which begins at the area centralis prenatally and spreads over the retina in a horizontally elongated wave postnatally. The elongation and orientation of ganglion cell dendritic fields were correlated with the geometry of this wave of maturation. Dendritic competition can account for the systematic dendritic displacement but not for dendritic elongation and orientation which must, therefore, be accounted for by another mechanism which these results indicate is related to the wave of maturation.