The Glial Perspective on Sleep and Circadian Rhythms.

While neurons and circuits are almost unequivocally considered to be the computational units and actuators of behavior, a complete understanding of the nervous system must incorporate glial cells. Far beyond a copious but passive substrate, glial influence is inextricable from neuronal physiology, whether during developmental guidance and synaptic shaping or through the trophic support, neurotransmitter and ion homeostasis, cytokine signaling and immune function, and debris engulfment contributions that this class provides throughout an organism's life. With such essential functions, among a growing literature of nuanced roles, it follows that glia are consequential to behavior in adult animals, with novel genetic tools allowing for the investigation of these phenomena in living organisms. We discuss here the relevance of glia for maintaining circadian rhythms and also for serving functions of sleep.