Whole-brain neural activity of individual neurons is visualized during animal behavior. Each sphere corresponds to the location of a recorded neuron. Each neuron’s size and color is indicative of calcium activity within the neuron and corresponds to percent change from baseline of the ratio R of GCaMP6s fluorescence intensity to RFP fluorescence intensity. A cartoon showing the outline of the head of the animal is marked in black. The animal’s position in the imaging arena is shown in the lower right. The animal’s behavior is shown in the lower left with the worm’s centerline indicated in blue. The instantaneous classification of the worm’s behavior based on an eigenworm analysis is indicated in the upper left. Worm 1 is shown. Video plays in real time.