High-speed large-scale 3D imaging of neuronal activity poses a major challenge in neuroscience. Here, we demonstrate intrinsically simultaneous functional imaging of neuronal activity at single neuron resolution for an entire Caenorhabditis elegans as well as for the whole-brain of larval zebrafish. Our technique captures dynamics of spiking neurons in volumes of ~700 μm x 700 μm x 200 μm at 20 Hz and its simplicity makes it an attractive tool for high-speed volumetric calcium imaging.