Project Summary/Abstract: Core 5, Optical Instrumentation The Optical Instrumentation Core will develop, implement, support, integrate, and improve optical and peripheral instrumentation, ensuring that our researchers have the best available technology. The overall aim of this U19 collaboration is to elucidate how working memory and decision-making are supported by interacting neurons and brain regions. To achieve this goal, our research projects require methods for large-scale recording and perturbation of neural activity. These methods depend on optical instrumentation, such as multi-photon microscopes, laser-based optogenetic perturbation systems, and widefield microscopy. Our experiments also rely on equipment that generates and controls, in real time, the virtual-reality environment in which the animals perform tasks. To take full advantage of the new technologies in the BRAIN Initiative, we will innovate and upgrade instrumentation and methods as the cutting edge of the field moves forward. The core’s first aim will be to implement, support, and improve two-photon and three-photon microscopes, which are used for calcium imaging and integrated with our mouse behavioral setups. We will maintain four mid-range field of view, two-photon microscopes, along with our mesoscope, which can image from two or more widely separated regions or layers at a high effective rate. This mesoscope is our core instrument for studying neural interactions between non-adjacent regions. We will also implement a recently developed technique that greatly increases the number of neurons simultaneously recorded. Finally, we will maintain and upgrade our three-photon microscope, used to image below cortex and in deep areas, and also to provide vasculature imaging for registering calcium imaging with electron microscopy. The second aim will be to support and improve widefield-imaging instrumentation. We will maintain a custom widefield microscope based on a back-to-back objective system for use with our mouse virtual-reality systems and integrate it into new behavioral systems as needed. This instrument is used to map boundaries of visual areas and the flow of neural activity via calcium imaging at the mesoscopic scale. The third aim will be to implement, support, and improve our combined optogenetic and imaging instrumentation. We built an instrument for simultaneous two-photon imaging and single-cell, two-photon photostimulation. In addition, we are redesigning an instrument we developed that combines cellular-resolution optogenetic perturbation of multiple cells simultaneously with large-scale calcium imaging of neural populations, which will be used to study how an animal's behavior is affected by changes in the sequences of neural activation during behavioral tasks. In summary, the Optical Instrumentation Core will provide seamless support for microscopy and virtual-reality experiments within all the research projects. More broadly, we expect that widespread avai...