Abstract: Electroencephalogram (EEG) is the super-imposed electrical signals at the scalp electrodes generated from neuronal activity. The combined signals of EEG and electromyogram (EMG) can be used to identify sleep and wake states. Therefore, factors affecting the neuronal activity could possibly modulate the state of sleep and wake. It has been well-defined in the past decades that postsynaptic neuronal activity is mediated by neurotransmitters release from presynaptic neurons. Neural circuits have been proposed to be the structural basis and functional system that regulate sleep-wake. Beside presynaptic inputs, neuronal activity can also be mediated by extracellular environment. All cellular elements of the central nervous system (CNS) are consistently exposed to the interstitial milieu. The interstitial ion compositions can affect action potential firings, neurotransmitter release, and synaptic transmission. The super-imposed single neuronal electrical activity will eventually integrate the whole brain state shift. Frontier studies suggest that the interstitial ion compositions could mirror or drive state transitions, such as, sleep, wakefulness and locomotion. Here we provide an literature review of the roles of interstitial ions in regulating neuronal activity, as well as sleep and wake state maintenances and transitions.

Key words: ion, sleep, wake, neuronal activity, extracellular microenvironment