Project Summary A fundamental aspect of our existence is the fact that we live in a spatially extended world. To survive and flourish in this world, we must have some method for navigating efficiently from place to place. The current project focuses on the neural mechanisms that underlie landmark- based navigation (LBN)—navigation that is guided by spatially stable elements of the environment. To implement LBN, a person must be able to 1) perceive the local environment, 2) use features of the local environment to determine their location and orientation in the world, and 3) plan a route that takes them from their current location to their navigational goal. In previous funding periods, we have used functional magnetic resonance imaging (fMRI) and other methods to identify regions of the human brain that mediate these operations and to assign functional roles to these regions. Now we seek to integrate these findings to understand how these neural/cognitive components work together to implement LBN during realistic navigational episodes. In aim 1 we will identify the spatial representations that are simultaneously active in the human brain during dynamic navigation, including representations of location and heading, and representations of the navigational goal. In aim 2 we seek to understand the remapping mechanisms that allow a navigator to negotiate a complex world that contains multiple local environments. In aim 3 we will delineate the reorientation mechanisms that allow a navigator to establish (or re-establish) their sense of place and direction after losing their bearings. Together, these operations—knowing where we are in the world and the location of our goal, distinguishing between different spatial environments, and recovering our bearings when we are disoriented—constitute core elements of spatial navigation. Understanding the neural mechanisms that underlie these elements would be a major and sustained intellectual advance in an area that has long been a central topic of investigation in psychology and neuroscience.