An optical design enabling lightweight and large field-of-view head-mounted microscopes

Here we present a fluorescence microscope light path that enables imaging, during free behavior, of thousands of neurons in mice and hundreds of neurons in juvenile songbirds. The light path eliminates traditional illumination optics, allowing for head-mounted microscopes that have both a lower weight and a larger field of view (FOV) than previously possible. Using this light path, we designed two microscopes: one optimized for FOV (~4 mm FOV; 1.4 g), and the other optimized for weight (1.0 mm FOV; 1.0 g). This dataset includes the calcium imaging data from our microscope optimized for weight. For this experiment, we stereotactically located a region of the mouse brain at coordinates associatied with primary visual and somatosensory regions, performed approximately 20 viral injections of GCaMP7f across a 4-mm-diameter region of cortex, and then implanted a 4-mm-diameter glass window in the skull. After letting each mouse recover, we installed our head-mounted microscope and allowed it to freely explore a circular maze while recording calcium activity for several minutes.