Project Summary: Core 4, Brain Registration and Pathway Tracing Working memory, the ability to temporarily hold multiple pieces of information in mind for manipulation, is central to virtually all cognitive abilities. This multi-component research project aims to comprehensively dissect the neural circuit mechanisms of this ability across multiple brain areas. The behavior to be studied is a type of decision-making task that is based on the gradual accumulation of sensory evidence and thus relies on working memory. A full understanding of how this behavior relates to this brain function requires explanation at multiple levels: from neural activity in particular regions to how those regions interact in brain-wide networks via specific pathways. These levels of analysis require distinct technical approaches, which are often difficult to relate to one another rigorously. This Core will promote rigor and reproducibility in the proposed research by producing an anatomical framework to standardize and compare the various types of data that will be collected. The facility will serve several essential functions in building a broad integrative structure for the project. First, it will produce standardized functional maps that will be used to accurately determine the boundaries of visual cortical regions before cellular-resolution imaging or inactivation studies. Second, it will register all studied brain areas into an anatomical context that includes connectivity and functional significance. Automated cell-recognition methods will be used to survey directly imaged regions and indirectly connected regions, and to classify neurons and other objects of interest. Third, it will support long-distance tracing across synapses to identify paths of connectivity between distant brain regions involved in evidence accumulation. Fourth, it will organize this information in a relational database that links all the experiments, in a format that can be shared with the neuroscience research community. As technologies for functional mapping, registration, and tracing advance over time, this facility will evaluate new methods, adopt those that will substantially improve the Core’s capabilities, and train project personnel in their use. Taken together, these functions are essential for placing recorded and perturbed neural activity into a brain-wide anatomical context, which will enable the integration of information produced by individual experiments and techniques into a coherent theoretical framework.