Watchful Waking

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Science  01 Mar 2002:
Vol. 295, Issue 5560, pp. 1603
DOI: 10.1126/science.295.5560.1603a

Sleep is traditionally thought to consist of two states: slow-wave sleep (SWS) alternates with periods of rapid eye movement (REM) sleep. These two states can easily be identified in hippocampal and neocortical EEG recordings by their distinctive activity patterns.

Jarosiewicz et al. describe a third physiological state that can consume up to 20% of overall sleep in the rat. In the hippocampal EEG, they observed a repeated pattern during sleep of small-amplitude irregular activity (S-SIA). During this state, the EEG is low in amplitude, and a small subpopulation of neurons (3 to 5% of the total cells) is active while the other cells remain virtually silent. The active cells display the features of pyramidal (complex spike) neurons and the characteristics of place cells, which denote a rat's location within its environment. The S-SIA appears several times within periods of SWS and immediately after every REM episode. The authors hypothesize that during S-SIA the animal may take in and process information from the sensorium without immediately acting on it, in contrast to SWS (which resembles drowsy waking states in exhibiting large-amplitude irregular activity) and REM or dreaming sleep (which exhibits the strong 7 to 8 hertz theta activity associated with active waking exploration). — PDS

J. Neurosci.22, 1373 (2002).

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