Sleep Analysis in Adult C. elegans Reveals State-Dependent Alteration of Neural and Behavioral Responses

Sleep, a state of quiescence associated with growth and restorative processes, is conserved across species. Invertebrates including the nematode Caenorhabditis elegans exhibit sleep-like states during development, satiety, and stress. Here, we describe behavior and neural activity during sleep and awake states in adult C. elegans hermaphrodites using new microfluidic methods. We observed effects of fluid flow, oxygen, feeding, odors, and genetic perturbations on long-term sleep behavior over 12 h. We developed a closed-loop sleep detection system to automatically deliver chemical stimuli to assess sleep-dependent changes to evoked neural responses in individual animals. Sleep increased the arousal threshold to aversive stimulation, yet the associated sensory neuron and first-layer interneuron responses were unchanged. This localizes adult sleep-dependent neuromodulation within interneurons presynaptic to the premotor interneurons, rather than afferent sensory circuits. However, sleep prolonged responses in appetitive chemosensory neurons, suggesting that sleep modulates responsiveness specifically across sensory systems rather than broadly damping global circuit activity.