Project Summary Few structures in the brain are as prominent, yet poorly understood, as the pulvinar nucleus of the thalamus. The pulvinar is both large and complex, having undergone more expansion with primate evolution than any other thalamic nucleus. Based on its reciprocal connections with the full extent of the visual hierarchy, from primary visual cortex through inferotemporal cortex, the pulvinar is strategically positioned to influence and facilitate the processing of visual signals in the brain. Despite the prominence of the pulvinar and its strategic connections, we know remarkably little about how the pulvinar contributes to vision. The primary goal of the experiments presented in this proposal is to determine how the primary visual cortex and the pulvinar interact to influence visual processing. The study involves two sets of experiments. The first major series of experiments will identify pulvinar neurons that receive direct input from primary visual cortex, characterize their physiology, and test the hypothesis that primary visual cortex drives pulvinar activity. It will also determine the role of cortico-pulvinar pathways in stimulus detection. The second series of experiments will determine the influence of pulvinar activity on cortical network interactions and spatial attention. Given the severe financial and quality-of-life consequences that follow from disruption in the ability of thalamus and cortex to communicate properly with each other, such as occurs with many forms of epilepsy and illnesses affecting vision and corticothalamic function, it is important that we understand how the thalamus and cortex interact to meet the processing needs of the brain.