MiniFAST: A sensitive and fast miniaturized microscope for in vivo neural recording

Abstract

Observing the activity of large populations of neurons in vivo is critical for understanding brain function and dysfunction. The use of fluorescent genetically-encoded calcium indicators (GECIs) in conjunction with miniaturized microscopes is an exciting emerging toolset for recording neural activity in unrestrained animals. Despite their potential, current miniaturized microscope designs are limited by using image sensors with low frame rates, sensitivity, and resolution. Beyond GECIs, there are many neuroscience applications which would benefit from the use of other emerging neural indicators, such as fluorescent genetically-encoded voltage indicators (GEVIs) that have faster temporal resolution to match neuron spiking, yet, require imaging at high speeds to properly sample the activity-dependent signals. We integrated an advanced CMOS image sensor into a popular open-source miniaturized microscope platform. MiniFAST is a fast and sensitive miniaturized microscope capable of 1080p video (1920x1080 pixels), 1.5 {micro}m resolution, frame rates up to 500 Hz (achieved with windowing: 1920 x 55 pixels height) and high gain ability (up to 70 dB) to image in extremely low light conditions. We report results of [~]300 Hz in vivo imaging of freely behaving transgenic Thy1-GCaMP6f mice, high speed 500 Hz in vitro imaging of a GEVI and in vivo GEVI imaging in head-fixed mice. Our results extend miniaturized microscope capabilities in high-speed imaging, high sensitivity and increased resolution, opening the door for the open-source community to use fast and dim neural indicators.