A miniaturized integrated fluorescence microscope was developed for high-speed cellular-level imaging in active mice. The device, weighing 1.9 g, uses mass-producible components including semiconductor light sources and sensors. It enables imaging across ~0.5 mm² areas, allowing concurrent tracking of Ca²⁺ spiking in >200 Purkinje neurons across nine cerebellar microzones. During mouse locomotion, individual microzones exhibited large-scale, synchronized Ca²⁺ spiking, a mesoscopic neural dynamic previously unobserved. The microscope's design, based on micro-optics and semiconductor optoelectronics, offers advantages over fiber-optic microscopes in optical sensitivity, field of view, resolution, mechanical flexibility, cost, and portability. It allows for distributed use across many animals and enables diverse applications such as portable diagnostics or microscope arrays for large-scale screens. The microscope's optical design includes a blue LED, a drum lens, and a GRIN objective lens, enabling high-resolution imaging with a field of view of 600 μm × 800 μm and a lateral resolution of ~2.5 μm. It tracks erythrocyte speeds and capillary diameters with 2-s time-resolution, revealing that only a spatially scattered minority of capillaries significantly changed diameters and flow speeds during locomotion. The device also tracks Ca²⁺ spiking in up to 206 individual cerebellar Purkinje neurons, with improved throughput allowing lower illumination power and longer recording times without photobleaching. This enabled the initial analysis of higher-order spiking correlations among Purkinje neurons in freely behaving animals, revealing synchronized Ca²⁺ spiking during motor behavior within individual cerebellar microzones. The microscope's capabilities were tested in live animals by imaging cerebral microcirculation in behaving mice, revealing that locomotor states evoked increases in flow speeds and capillary diameters compared to resting periods. The device also enabled the first analysis of higher-order correlations in these cells' dynamics in freely behaving animals, showing that predominantly during motor activity, large cohorts of up to >30 Purkinje neurons within individual microzones fired synchronous Ca²⁺ spikes. The microscope's portability, low cost, and simple electronics make it suitable for use in locations inhospitable to conventional microscopy. It also enables in vitro applications such as fluorescent cell counting and detection of tuberculosis bacilli in fluorescence assays. The device's design allows for mass production and is compatible with a range of in vitro applications, including portable fluorescence assays and high-throughput screening. The microscope's integration of optical and electronic components, along with its ability to track neural activity in freely behaving animals, represents a transformative technology for brain imaging and other applications.A miniaturized integrated fluorescence microscope was developed for high-speed cellular-level imaging in active mice. The device, weighing 1.9 g, uses mass-producible components including semiconductor light sources and sensors. It enables imaging across ~0.5 mm² areas, allowing concurrent tracking of Ca²⁺ spiking in >200 Purkinje neurons across nine cerebellar microzones. During mouse locomotion, individual microzones exhibited large-scale, synchronized Ca²⁺ spiking, a mesoscopic neural dynamic previously unobserved. The microscope's design, based on micro-optics and semiconductor optoelectronics, offers advantages over fiber-optic microscopes in optical sensitivity, field of view, resolution, mechanical flexibility, cost, and portability. It allows for distributed use across many animals and enables diverse applications such as portable diagnostics or microscope arrays for large-scale screens. The microscope's optical design includes a blue LED, a drum lens, and a GRIN objective lens, enabling high-resolution imaging with a field of view of 600 μm × 800 μm and a lateral resolution of ~2.5 μm. It tracks erythrocyte speeds and capillary diameters with 2-s time-resolution, revealing that only a spatially scattered minority of capillaries significantly changed diameters and flow speeds during locomotion. The device also tracks Ca²⁺ spiking in up to 206 individual cerebellar Purkinje neurons, with improved throughput allowing lower illumination power and longer recording times without photobleaching. This enabled the initial analysis of higher-order spiking correlations among Purkinje neurons in freely behaving animals, revealing synchronized Ca²⁺ spiking during motor behavior within individual cerebellar microzones. The microscope's capabilities were tested in live animals by imaging cerebral microcirculation in behaving mice, revealing that locomotor states evoked increases in flow speeds and capillary diameters compared to resting periods. The device also enabled the first analysis of higher-order correlations in these cells' dynamics in freely behaving animals, showing that predominantly during motor activity, large cohorts of up to >30 Purkinje neurons within individual microzones fired synchronous Ca²⁺ spikes. The microscope's portability, low cost, and simple electronics make it suitable for use in locations inhospitable to conventional microscopy. It also enables in vitro applications such as fluorescent cell counting and detection of tuberculosis bacilli in fluorescence assays. The device's design allows for mass production and is compatible with a range of in vitro applications, including portable fluorescence assays and high-throughput screening. The microscope's integration of optical and electronic components, along with its ability to track neural activity in freely behaving animals, represents a transformative technology for brain imaging and other applications.