The ability to analyze the trajectories of objects moving though many degrees of visual space is essential to a number of biologically important behaviors in humans and other vertebrates. However, most investigations of the neural mechanisms that underly motion analysis have so far focused on retinal ganglion cells or cortical neurons involved only in the analysis of motions occurring within a few degrees of visual space. Extracellular and behavioral studies on primates have provided some insights into the sequence of cortical areas involved in the more global aspects of motion analysis, but there have been no detailed models dealing with the neural mechanisms of global motion analysis. The proposed research takes advantage of the relative simplicity of the central visual pathways in turtles and a powerful in vitro preparation of turtle visual cortex to provide initial quantitative data on the physiological properties of geniculocortical afferents, intracortical projections within visual cortex and cortical inhibitory interneurons. Intracellular recording techniques will be used in the in vitro preparation to characterize (1) the spatial patterns by which axons from the dorsal lateral geniculate complex activate neurons in visual cortex, (2) the spatial patterns by which intracortical axons, employing a form of synaptic potentiation mediated by NMDA receptors, access a form of temporal storage essential to global motion analysis and (3) the spatial distribution of GABAergic interneurons and inhibitory postsynaptic potentials thought to be involved in habituation to visual stimuli. These data will be used in the context of a model of the neural mechanisms of global motion detection being developed in our laboratory.
