While advances have been made in characterizing the synaptic organization and visual response properties of the pulvinar nucleus, its'exact contributions to the coding of visual signals have remained elusive. The proposed experiments are designed to answer fundamental questions regarding the projection from the pulvinar nucleus to the striate cortex. Using novel combinations of optogenetics, tract tracing and in vitro whole cell recordings, we will determine which cortical cell types are activated by pulvinocortical terminals, and the frequency dependency of pulvinocortical responses. We will then use optogenetics and in vivo intrinsic optical imaging to determine whether inputs from the pulvinar nucleus change cortical receptive field properties. Tree shrews (tupaia belangeri) will be used as the experimental model because the circuitry of tree shrew striate cortex is well defined and similar to that of primates, and in vivo intrinsic optical imaging of the tree shrew striate cortex provides a convenient method to monitor global changes in receptive field properties. The proposed experiments should contribute to our understanding of the construction and modulation of striate cortex response properties, and how the pulvinar nucleus contributes to vision. PUBLIC HEALTH RELEVANCE: The proposed experiments should contribute to our basic scientific understanding of the construction and modulation of V1 response properties relevant to the treatment of disorders such as strabismus and amblyopia. The experiments should also reveal fundamental information regarding the function of the pulvinocortical projections relevant to the treatment of disorders that are known to affect the pulvinar nucleus, such as schizophrenia.