The Development of Orientation and Direction Selectivity in the Primary Visual Cortex and Lateral Geniculate Nucleus

Classic studies of lateral geniculate nucleus (LGN) and visual cortex (V1) in carnivores and primates have found that a majority of neurons in LGN exhibit a center-surround organization, while V1 neurons exhibit strong orientation selectivity and, in many species, direction selectivity. This has led to the prevailing model that orientation and direction selectivity are computed anew in the cortex. However, recent work in mice has indicated that direction-selective cells from the retina project directly to the LGN, and some species may have orientation and direction selectivity in the LGN. To examine whether LGN cells make a substantial contribution to cortical orientation selectivity, we examined orientation and direction selectivity in LGN and V1 neurons of a highly visual diurnal rodent: the gray squirrel. Although direction selectivity was weak overall, LGN layers 3abc exhibited elevated direction selectivity index values compared to LGN layers 1 and 2. These results suggest that, for central visual fields, the contribution of orientation-and direction-selective channels from the LGN to V1 is small in the squirrel. However, orientation and direction selectivity that may be found transiently during development, and might seed cortical orientation or direction selectivity, has yet to be studied. We performed electrophysiological records on ferrets at eye opening (P30-35). Preliminary results indicate that the developing LGN may exhibit some orientation and direction selectivity. Future experiments will involve collecting more data from ferrets early in development, at around the time of opening. The primary visual cortex (V1) is the first site in the primate visual system where there are close correspondences between the response properties of neurons and perceptual behaviors of the animal, making it a critical area for the study of cortical circuitry. Two fundamental response properties of neurons in V1 are the selectivity to stimulus orientation and direction. In this work, we will review the visual pathways, development, and models for the circuit origins of these computations in V1 and its antecedent structures, in particular the lateral geniculate nucleus (LGN). Finally, we will describe the direction of our research addressing this field. Orientation selectivity, the preferential response of neurons to a stimulus (such as a bar of light) oriented at a particular angle, was first described in the primary visual cortex of the cat and has since been found in V1 in all examined mammals (Hubel and display a further type of selectivity for the stimulus direction of motion, or direction selectivity, in which the …