The long-term objective of this research is to determine how visual information is encoded and transformed in the brain. To achieve this goal, it is necessary to understand neural wiring patterns within the visual pathway. The traditional approach has involved the study of single neurons and their synaptic connections, but relatively little is known about how a given cell's function is correlated with that of others. Yet, simultaneous firing patterns of groups of cortical neurons must underlie visual perception. The proposed project will utilize an electrophysiological approach to determine response properties of small groups of cortical neurons, as well as single cells. Previous studies have focused primarily on spatial aspects of receptive field structure. The work planned in this proposal examines both temporal and spatial response parameters to obtain a more complete description of visual cortical function. The analysis provides receptive field profiles in two dimensions of space and one dimension of time. In addition, a new technique will be employed to obtain complete spatiotemporal maps of temporally correlated discharge from pairs of cells whose firing patterns are measured simultaneously. This analysis provides a powerful tool because it can show how the activity of one cell contributes to the spatiotemporal receptive field of another cell. These methods will be used to address the following specific projects. (1) Spatiotemporal information processing in binocular pathways will be examined with respect to the mechanism of binocular disparity encoding and the joint analysis of disparity and motion processing in complex cells. (2) The genesis of spatiotemporal receptive fields in the visual cortex will be explored by multiple cell analysis and by development of quantitative, physiologically plausible models that may be tested experimentally. (3) Spatiotemporal information processing in monocular pathways will be investigated with respect to four questions. (a) How are transient responses of cortical cells related to those of a steady-state nature? (b)What is the spatiotemporal organization of surround inhibition? (c) What mechanisms underlie plasticity of receptive field structure? (d) Are the receptive fields of nearby simple cells organized for phase encoding of visual images? These studies will reveal important aspects of spatiotemporal function in the retinogeniculocortical pathway. Eventually, this should lead to improvements in the diagnosis and treatment of visual disorders.
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