Project Summary For almost 50 years, scientists have investigated the relationship between eye movement control and the activity of neurons in the frontal eye field (FEF), superior colliculus (SC) and lateral intraparietal area (LIP). The general findings of these studies have been that neurons in all three areas are important for eye movement behavior, but they have identified very few differences between the areas, implying that they all do similar things. Recently, a small number of labs have started using more naturalistic free-viewing behavioral tasks and have found a number of substantive differences in neural responses across these areas, suggesting that they each play a unique role. Based on these data, we formed a hypothesis about the roles of each area and how they may function as a network to generate behavior. Briefly, we have proposed that LIP acts as simple priority map that is constantly accessible, FEF activity controls the timing of saccades and SC activity represents the final decision about where to look. In addition, a subset of neurons in FEF keeps track of where the animal has looked. Building on this previous work, the current proposal has two main aims. The first is to fill in two gaps of our knowledge that are essential in finalizing our hypothesis. As part of this aim, we propose to record from SC neurons in a free viewing visual foraging task to confirm that SC activity is not affected by stimulus identity in ongoing search. We also propose to record from FEF neurons in an even more natural version of our task to make sure that suppression we have previously seen during maintained fixation is a mechanism for controlling the timing of eye movements as opposed to a mechanism related to reward expectation. The results of these studies will refine our hypothesis and set us up for the second main aim of the proposal, which is to test whether our hypothesized roles are functionally valid. This second aim is broken into 3 components. In each, we will causally test aspects of our hypothesis. In the first experiment, we will microstimulate LIP at different times to test whether the suppression we have identified in FEF controls the flow of information from LIP to guide saccades. In the second experiment, we will inactivate LIP while recording from FEF and SC. The results of this experiment will test the hypothesis that LIP activity drives saccadic behavior via FEF and SC and, if it does not, these recordings should identify which area does play a role in guiding behavior. In the third experiment, we will inactivate FEF while recording from SC. This will allow us to test three additional aspects of our hypothesis: whether FEF activity guides behavior and whether this is also represented in SCI; whether the tracking signal in FEF in functionally relevant; and whether the activity in FEF is involved in controlling the temporal flow of saccades. These results will solve a decades-long question of why we have multiple brain areas by ...