A robotic multi-armed two-photon microscope for imaging neural interactions across multiple brain areas

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Abstract Among the BRAIN Initiative’s most important achievements are the genetic identification of many new neurons- types and the creation of genetic tools to access these cell types. However, uncovering the functional roles of these neuron types and how they cooperate across brain areas to generate mammalian behavior remains an outstanding challenge. Thus, inventing ways to monitor how large populations of genetically identified neurons interact across multiple regions of the brain is crucial if we are to comprehend global brain dynamics. Today, electrical recording methods can track neural activity across multiple areas but cannot easily target neurons of specific types. Widefield and two-photon mesoscopes can image the dynamics of identified neuron-types across millimeter-scale regions of cortical tissue but cannot access the distributed sets of cortical and subcortical regions that comprise the major nodes of the brain’s sensory, cognitive, or motor circuits. To clear this impasse, we invented the ‘Octopus’, a robotic imaging system with multiple articulated optical arms, each a two-photon microscope, that can be flexibly positioned around the brain to record neural activity concurrently in multiple superficial or deep areas of a head-restrained behaving rodent or primate. We designed, built, and tested an initial version of the Octopus with 4 arms, each of which has 5 mechanical degrees of freedom and a micro-optic probe at its tip for two-photon imaging. The design of the arms is based on ideas from surgical robotics and uses remote center-of-motion kinematics to provide a versatile repertoire of robotic arm movements. Using this system, a visual neuroscientist can concurrently image neural activity in the lateral geniculate nucleus, visual cortex, superior colliculus, and pulvinar, and a motor neurophysiologist can image activity in the motor cortex, basal ganglia, cerebellum, and motor thalamus. In this project, we will enhance the optical and mechanical design of each Octopus arm and prepare the system for wide dissemination through open-source and commercial routes. Each arm will gain the optical functionality of a state-of-the-art, two-photon microscope for imaging large-scale neural ensemble activity. Specifically, each arm will incorporate optogenetics and allow dual-color two-photon imaging over an 800-µm- wide field of view. These capabilities will allow neuroscientists to monitor two genetically identified neuron- types in each of 4 brain areas, to perturb the dynamics of these cells with optogenetics, and to observe the effects of these manipulations on animal behavior and activity in the other 3 areas. We will also streamline the mechanical design to simplify the initial assembly of the Octopus for new users and to endow the robot arms with additional dexterity. The new design will also be motorized and will provide users with highly intuitive means of precisely steering the robot arms. Finally, to iteratively improve the performance and usability of the Octopus and to validate its readiness for dissemination as a groundbreaking new technology, we will work closely with 7 beta-tester labs to implement multi-area neural imaging studies in awake behaving mice and marmosets.