An understanding of neuronal circuitry within the brain has important implications for diseases of circuits such as Alzheimer's and Parkinson's diseases. The visual system is an ideal model in which to study neural circuitry because it is precisely organized and much is known about its cellular and compartmental components. This proposal examines the function and anatomy of an important, yet elusive, pathway within the visual system: the corticogeniculate feedback pathway. Geniculate-projecting neurons in primary visual cortex which constitute the corticogeniculate pathway in the visual system will be studied using a three-tiered experimental approach. The first experiment involves recording from individual geniculate-projecting neurons within primary visual cortex in the conscious animal in order to elucidate their function in vivo. In the second experiment, individual geniculate-projecting neurons are identified by their physiology and labeled such that their sub-laminar location can be determined. The third experiment involves identifying the locations and morphological identities of geniculate-projecting neurons targeting specific regions of the lateral geniculate nucleus.