Focus-tunable microscope for imaging small neuronal processes in freely moving animals

Miniature single-photon microscopes have been widely used to image neuronal assemblies in the brain of freely moving animals over the last decade. However, these systems have important limitations for imaging in-depth fine neuronal structures. We present a subcellular imaging single-photon device that uses an electrically tunable liquid crystal lens to enable a motion-free depth scan in the search of such structures. Our miniaturized microscope is compact ( 10 mm × 17 mm × 12 mm ) and lightweight ( ≈ 1.4 g ), with a fast acquisition rate (30–50 frames per second), high magnification ( 8.7 × ), and high resolution (1.4 μm) that allow imaging of calcium activity of fine neuronal processes in deep brain regions during a wide range of behavioral tasks of freely moving mice.