Over the past decades, the combination of anatomical and physiological techniques has generated a detailed map of the main connections made by cortical and subcortical structures within the brain. The challenge remains to discover their function. Understanding the function of a major connection requires collecting many pieces of information through well-targeted objectives. This proposal will study the properties of two major types of connections within the visual pathway (corticocortical and corticothalamic) by focusing on two main questions: What cell types are involved in each connection? What is the strength of the connections as estimated from the correlated firing they generate? First, experiments will be done to investigate whether corticocortical and corticothalamic connections follow different wiring strategies (e.g. cell types involved, quality of the receptive-field match between connected cells, etc.). Second, the relative strength of corticortical, thalamocortical and corticothalamic connections will be estimated by measuring the correlated firing generated between inputs and targets by each of these connections. Third, experiments will be done to investigate the role of the corticothalamic pathway in modulating different types of geniculate synchrony (e.g. synchrony generated within the retina, synchrony generated among geniculate cells that share a retinal afferent, other types of synchrony). All these questions will be addressed by combining modern techniques of simultaneous recordings and automatic receptive field mapping with more classical tools such as cross-correlation analysis, electrical microstimulation and pharmacological reversible inactivation of restricted brain regions. The study of the properties of corticocortical and corticothalamic circuits is important to understand neural mechanisms involved in visual processing. A precise knowledge of these mechanisms could eventually help to prevent and treat different forms of visual disorders.