Sleep induction through ion changes How do we switch from sleep to arousal and back? Ding et al. found that a combination of modulatory neurotransmitters influenced the levels of extracellular ions in the brain (see the Perspective by Landolt and Holst). This influence was not driven by changes in local neuronal firing, suggesting direct effects of the neuromodulators on extracellular ion composition. However, these changes in interstitial ion levels could switch a brain from wakefulness to sleep. Changes in extracellular ions may thus be a cause, rather than a consequence, of sleep/wake-dependent changes in neuronal activity. Science , this issue p. 550 ; see also p. 517

Changes in the composition of brain interstitial ions control the sleep-wake cycle