In a famous example of studying a sleep-like behavior in a phylogenetically ancient model organism, Seymour Benzer – physicists, biologists and one of the founders of the field of molecular biology of behavior – studied the cycles of quiescence of the fruit fly Drosophila. He showed that the period gene is a key regulator of the circadian clock, which is thought to have a role in regulating sleep in mammals. Recently, two additional pathways were shown to play a role in regulating sleep-like behavior in fruit flies and sleep in mice, rabbits and hamsters: Epidermal Growth Factor (EGF) signaling and cyclic-Adenosine MonoPhosphate (cAMP) signaling.

The roundworm C. elegans is in many ways a simpler model organism than the fruit fly, and even more phylogenetically ancient. The worm develops through four larval stages before it reaches adulthood. At the end of each of these stages it exhibits a quiescent behavior called lethargus. David Raizen et al. recently demonstrated that lethargus bears behavioral similarities to sleep, such as reversibility (the worms “wake up”), sensory gating (an elevated threshold for responding to sensory stimuli) and homeostatic control (following deprivation, lethargus is resumed faster and “deeper”). Curiously, lethargus is also phase locked with cycles in the expression of the worm’s period-like gene. Moreover, EGF and cAMP signaling both appear to have roles in regulating lethargus that resemble their regulation of similar behaviors in flies and mammals. Taken together, these observations suggest a possible ~6×10⁸ year-old genetic link between these phenomena.

I will discuss the opportunities, challenges and risks of studying a sleep-like behavior using C. elegans as a model system. Time permitting, I will discuss some tools and ideas that physics can bring to the study of this everyday – in a sense, universal – natural phenomenon.