As animals navigate their environments, their nervous systems transition between different states of arousal, motivation, and mood that influence how sensory information is processed and how behaviors are generated. Steve Flavell investigates the neural mechanisms that generate these internal states, with a focus on the involvement of the distributed neuromodulatory systems that control the brain’s state. Flavell examines this problem in the roundworm C. elegans, using cell-specific genetic tools to monitor and perturb neurons throughout an entire nervous system whose synaptic connectivity is known. Flavell’s research aims to uncover mechanistic links between neuromodulation, brain-wide neural activity, and animal behavior.