Summary

Sleep, a complex phenomenon with an unknown function, is present in a wide range of animals, both vertebrates and invertebrates. Sleep definitions typically include at least two of three main criteria: behavioral, brain electrical activity, and the activation of certain genes. Additional collateral criteria may include metabolic changes, autonomic regulation, and involvement in learning and memory. While most vertebrates fulfill these criteria, invertebrates often do not because of anatomical and size constraints.

Crayfish are crustaceans that inhabit freshwater ecosystems globally. These animals have been extensively studied for their remarkable biological features, including their intricate nervous system, sensory capabilities, circadian rhythms, escape reflex, and complex behavior, such as sleep.

Crayfish sleep fulfills both behavioral and electrophysiological criteria defined for vertebrates. Research over the past 20 years has revealed neural correlates of crayfish sleep and potential similarities with sleep in other organisms, including humans. Understanding sleep in an invertebrate model like crayfish may provide valuable insights into the evolutionary origins and fundamental principles of sleep across diverse species.