In order to maintain proper brain function, neural activity often needs to be tightly coordinated within neuronal ensembles and across different brain regions. In this issue, three articles highlight new concepts that help to explain the functional importance of this coordination and how it is achieved.

In recent years, it has been shown that astrocytes, like neurons, are organized into networks. On page 87, Giaume and colleagues discuss the organization of astroglial networks, the rules that govern their intercellular communication through gap junction channels and the effects of such networks on coordinated neuronal activity.

Sleep has been shown to be important for the consolidation of memory. In an authoritative Review on page 114, Diekelmann and Born discuss how coordinated patterns of activity in different brain regions during slow wave sleep underlie the re-activation and redistribution of memory traces from the hippocampus to the neocortex.

Recently, schizophrenia has been associated with alterations in coordinated oscillatory activity in neurons. In the Review on page 100, Uhlhaas and Singer discuss the mechanisms that could lead to these deficits and how impaired oscillations might contribute to schizophrenia.

In summary, these articles highlight the importance of the coordination of neural activity across neuronal networks for brain function.

Finally, several theories have attempted to describe the principles by which the nervous system interacts with the world. In a Review on page 127 Karl Friston considers a number of global brain theories and discusses how the free-energy principle can unify these different perspectives on brain function.