FUNCTIONAL ANALYSIS OF RETINAL GANGLION CELLS

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The proposed experiments will examine fundamental aspects of visual information processing by the mammalian retina. Ganglion cells of the cat's retina may be separated into a small number of classes, or sub-systems, according to their visual characteristics and the central projection of their axons. Establishing the role each retinal sub-system plays is an important goal for understanding how the sensory and motor components of the visual system work. Knowing what and how each retinal sub-system performs, in turn, will provide a rational basis for future development of new techniques for the diagnosis and treatment of disorders such as optic neuritis, amblyopia and strabismus. The experimental approach to be adopted is based on the idea that the functional role of a ganglion cell is determined, at least in part, by its visual properties. The property of fundamental importance to be investigated is the detection of sinusoidal gratings. Not only are gratings useful for defining ganglion cell performance, they also serve as effective probes of the basic structure of receptive fields within the theoretical framework of Fourier analysis. Experiments will have two interrelated aims. First will be a comparative study of how the eight different classes of concentrically-organized ganglion cells (on/off, brisk/sluggish, sustained/transient) differ in their sensitivity to gratings. Representative cells of each class will be isolated for study with a microelectrode introduced into the eye of a paralyzed and anesthetized animal. Contrast sensitivity will be measured for a series of gratings which cover the full spectrum of spatial frequencies and orientations. Comparisons will be drawn between the performance of different types of cells at a fixed retinal location and also between cells of the same class but at different retinal locations. The second aim will be to investigate the relationship between functional receptive fields and structural dendritic fields. Anatomical descriptions of dendritic trees will be obtained from the stained, whole-mount preparation of the retina at the termination of neurophysiological observations. Specific cells which were studied functionally will then be identified by light microscopy and the results correlated with the form of the dendritic field. Particular features of interest will be the shapes of the fields and systematic patterns of asymmetry.