Modeling LGN responses during free-viewing: A possible role of microscopic eye movements in the refinement of cortical orientation selectivity

Neural activity appears to be essential for the normal develop-ment of the orientation-selective responses of cortical cells. It has been proposed that the correlated activity of LGN cells is a crucial component for shaping the receptive fields of cortical simple cells into adjacent, oriented subregions alternately re-ceiving ON- and OFF-center excitatory geniculate inputs. After eye opening, the spatiotemporal structure of neural activity in the early stages of the visual pathway depends not only on the characteristics of the environment, but also on the way the environment is scanned. In this study, we use computational modeling to investigate how eye movements might affect the refinement of orientation tuning in the presence of a Hebbian scheme of synaptic plasticity. Visual input consisting of natural scenes scanned by varying types of eye movements was used to activate a spatiotemporal model of LGN cells. In the pres-ence of different types of movement, significantly different pat-terns of activity were found in the LGN. Specific patterns of correlation required for the development of segregated cortical receptive field subregions were observed in the case of micro-movements, but were not seen in the case of saccades or static presentation of natural visual input. These results suggest an important role for the eye movements occurring during fixation in the refinement of orientation selectivity. Key words: visual development; microsaccade; natural visual experience; computer model; cat; visual fixation; Hebbian plasticity Since the discovery that high percentages of cells in the primary visual cortex of different mammal species respond preferentially to luminance edges with specific orientations (Hubel and Wiesel, 1962), the developmental origin of cortical orientation selectivity has been studied intensively. Substantial experimental evidenc