How does the activity of neurons give rise to cognitive phenomena such as short-term memory or decision-making? To address this question, we will take advantage of an experimental setup we have perfected over the course of a decade. In this setup, a rodent is allowed to navigate through a virtual reality world while we record the activity of many neurons in its brain at the same time. We can also use sophisticated genetic techniques to perturb the activity of neurons in the brain, allowing us to test models in a causal manner. The animals will perform such tasks as making decisions based on memories. We will analyze the data in collaboration with theoretical labs, which will bring statistical and mathematical expertise to the table. Because tasks such as making decisions based on memory cannot be explained by simple responses to sensory stimuli alone, we will be studying how the intrinsic activity of the brain—i.e., the brain state—affects choices. Because of the similarity of mammalian brains, we expect these insights to apply to humans as well.