ABSTRACT Perception and cognition arise from the coordinated activity of large networks of neurons spanning diverse brain areas. Understanding their emergent behavior requires large-scale activity measurements both within and across regions, ideally at single cell resolution. An integrative understanding of brain dynamics requires cellular-scale data across sensory, motor, and executive areas spanning more than a centimeter. In addition, functional interactions between brain areas vary with motivational state and behavioral goals, making data from freely moving animals particularly critical. Thus, a key goal is the ability to measure activity across the full extent of cortex at cellular resolution as animals engage in complex, cognitively demanding behaviors. However, conventional fluorescence microscopy techniques cannot meet the joint requirements of FOV, resolution, and miniaturization. Here, we propose a Computational Miniature Mesoscope (CM2) that will enable cortex- wide, cellular resolution Ca2+ imaging in freely behaving mice. The premise is that computational imaging leverages advanced algorithms to overcome limitations of conventional optics and significantly expand imaging capabilities. In our proof-of-principle system, we demonstrated single-shot 3D imaging across an 8x7mm2 FOV and 7µm resolution in scattering phantoms (Sci. Adv. 2020), and achieved single-cell resolution on histological sections. Our wearable prototype has now demonstrated visualization of sensory-driven neural activity across the 4x4mm2 main olfactory bulb in both head-fixed and freely moving mice. In this project we will: (Aim 1) advance CM2 hardware to achieve cortex-wide cellular resolution imaging. We will validate the hardware improvement on both phantoms and in vivo experiments. (Aim 2) Develop scattering-informed deep learning for fast and robust recovery of neural signals. We will validate the algorithm on in vivo experiments and benchmark against tabletop 1P and 2P measurements. (Aim 3) Cortex-wide, cellular-resolution Ca2+ imaging during social recognition in freely behaving mice. We will use CM2 to investigate the cross-area, network-scale activity dynamics that guide social interactions between familiar partners - one of the most integrative, multi-sensory, and cognitively demanding forms of neural processing. IMPACT ON PUBLIC HEALTH: This work will establish powerful enabling technology that greatly expands the scale of activity measurements possible in behaving animals, providing access to a wide range of questions about distributed cortical function. As a focused application, we will test the neural signatures of individual recognition during social behavior. We anticipate that our approach can be extended to a broader range of biological questions such as navigation, short- and long- term memory storage, and can potentially lead to new strategies for characterizing the disruptions in neural function that occur in psychiatric disease and neurodegenerative disorders.

NARRATIVE There remains a major unmet need for developing novel imaging platforms to visualize network-scale activity dynamics during complex, unrestrained behaviors. We propose to develop a novel head-mounted computational miniature mesoscope that applies computational imaging principle to enable recording cortex-wide Ca2+ dynamics with single-cell resolution of neural activities in freely behaving mice. We will apply this new technology to visualize the cross-area, network-scale activity dynamics that guide social interactions between familiar partners - one of the most integrative, multi-sensory, and cognitively demanding forms of neural processing.