A new view on post-receptoral signal processing in retino-geniculate pathways of humans.

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The results of the research performed in the frame of the first funding period showed that the electroretinogram (ERG) can reflect activity of the different photoreceptor types and of the major postreceptoral (parvo- and magnocellular; ON- and OFF-) retinal pathways. In addition, temporal, spectral and spatial properties of these retinal pathways were studied. For the first time, it was possible to study the physiology of the retina, with a relevance for visual perception, in vivo in human subjects.These data led to the following issues that will be studied in the applied project:An important goal of the project will be to use novel methods to study the signals that originate in the different photoreceptor types and in the major postreceptoral pathways. Novel stimulation (temporal white noise; TWN) and analysis (cross-correlation) techniques will developed and used to come a more complete description of the visual information processing in the retina. The TWN stimulation technique is extremely well suited to study the effects of mean luminance and stimulus intensity independently. The method can also easily be combined with the so-called silent substitution stimulation, with which single photoreceptor types can be stimulated. Neither the independent studies nor the combination with silent substitution is possible with the conventional ERG techniques.A second goal of the project is to extend the spatial measurements of the photoreceptor driven and pathway reflecting ERGs by using small stimuli at different retinal locations and by using multifocal stimulation. These experiments will elucidate the spatial distribution of the signals originating in the different photoreceptors and in the different retinal pathways. This work should ultimately lead to a functional image of the retina.A final goal will concentrate upon the question if cone distribution and retinal circuitries are generally the same in all primates. Therefore ERG experiments on non-human primates, in the laboratory of Prof. Laura Frishman at the University of Houston (USA), are planned. The contributions of ON- and OFF-pathways will be studied by using selective blockades of these pathways.