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

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 using image sensors with low frame rates, sensitivity, and resolution. Beyond GECIs, there are many neuroscience applications that 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.

We integrated an advanced CMOS image sensor into a popular open-source one-photon miniaturized microscope platform.

MiniFAST is a fast and sensitive miniaturized microscope capable of 1080p video ( $1920\times 1080\mathrm{pixels}$ ), $1.5\mu m$ resolution, frame rates up to 500 Hz (achieved with windowing: $1920\times 55\mathrm{pixels}$ height), and high gain ability (up to 70 dB) to image in extremely low-light conditions.

We report results of $\sim 300\text{-}\mathrm{Hz}$ 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.