The need for a simple animal model to understand sleep

Simple animal models have allowed biologists to apply the tools of modern m olecular genetics to such complex behaviors as circadian rhythms and long-t erm memory consolidation. The mechanisms and molecules discovered in these simple animals are evolutionarily conserved in other species, including mam mals. Sleep research lacks a simple animal model because criteria based on the electroencephalogram have been met only in birds and mammals. We argue that straightforward behavioral criteria could allow the identification of a sleep-like rest state that might be useful for molecular investigations t o understand the regulation and function of sleep. Candidate model systems are discussed, leading to the conclusion that several species have compleme ntary strengths. Specifically, techniques developed for larval zebrafish ca n be used to Visualize neural firing patterns in the living animal, and the fruit fly Drosophila melanogaster has been used successfully for molecular and genetic dissection of complex behaviors. We conclude with a hypothesis that one putative function of sleep, the optimization of neural plasticity , would also have adaptive value in simple organisms and might therefore be evolutionarily conserved. (C) 2000 Elsevier Science Ltd. All rights reserv ed.