A head-mounted open-source light field microscope for large volumetric Ca2+ imaging during exploratory and social behavior in mice.

Capturing neuronal activity during natural behaviors in unrestrained animals is critical for understanding brain function, yet existing imaging systems struggle to combine volumetric field-of-view (v-FOV), high resolution, depth, and usability. We present MiniLFMv2, a lightweight, next-generation miniaturized light field microscope enabling volumetric imaging with a v-FOV of ⌀1 × 0.2 mm3, volume rates of up to 30 Hz and depth to ∼350-400 μm. MiniLFMv2 achieves near-diffraction-limited performance, with a working distance of 1 mm. Its custom aspheric lenses and electrically tunable lens eliminate the need for GRIN optics, improving compatibility with cranial window imaging. Applying MiniLFMv2 in freely moving mice, we captured activity from hundreds of parietal cortex neurons at depths up to ∼400 μm with minimal impact on mobility. During exploratory and social behaviors, we identified subpopulations selectively tuned to locomotion, rearing, and social investigation. MiniLFMv2 offers a powerful tool for investigating neural dynamics during naturalistic and social behaviors.