BASICS The Art of Entrainment

Abstract The circadian system actively synchronizes the temporal sequence of biological functions with the environment. The oscillatory behavior of the sys-tem ensures that entrainment is not passive or driven and therefore allows for great plasticity and adaptive potential. With the tools at hand, we now can con-centrate on the most important circadian question: How is the complex task of entrainment achieved by anatomical, cellular, and molecular components? Understanding entrainment is equal to understanding the circadian system. The results of this basic researchwill helpus tounderstand temporal ecologyandwill allow us to improve conditions for humans in industrialized societies. Key words circadian, oscillator theory, clock genes, clock proteins, feedback loops, photoperiodism, PRC WHAT’S THE PROBLEM? The ability to oscillate with a self-sustained ampli-tude in constant conditions is regarded as the circa-dian clock’s central quality, yet in nature, the opportu