CRCNS: Collaborative Research : How is Information Coded in Turtle Visual Cortex ?
Visual stimuli evoke a propagating wave of activity in the visual cortex of freshwater turtles. Preliminary work suggested that information about the position of stimuli in visual space is coded in the spatiotemporal dynamics of these waves. Effectively, there may be a map of visual space to the dynamics of the visual cortex. This hypothesis is being examined in a collaborative effort involving three laboratories. David Senseman in San Antonio is using voltage sensitive dye methods to record the waves produced by presenting spots of light at 35 spots on the retina. These studies will characterize the features of the map based on repeated presentations of stimuli at 35 loci. Philip Ulinski in Chicago is developing a large-scale model of the visual pathway of turtles. Models of individual retinal ganglion cells that combine both classic filter-based approaches to modeling ganglion cells, with compartmental modeling of ganglion cells are being constructed. They are being used to construct 35 patches of a model retina that match the 35 loci. Physiological studies of the biophysics of neurons in the lateral geniculate complex of turtles are being carried out. They are used to develop a model of the lateral geniculate complex, which is the last step in modeling the retino-geniculate-cortical pathway. Bijoy Ghosh in St. Louis is developing refined estimation techniques that allow the position of a visual stimulus to be estimated from the dynamics of the cortical waves. This work is providing the mathematical framework needed to characterize a potential map of visual space to the dynamics of the wave. This work is significant because it is characterizing a novel method of coding information in visual cortex that may apply to higher order cortical areas in mammals, as well as turtles.
