Local sleep in awake rats

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• Olcese, Umberto
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• Hanlon, Erin C.
;
• Nir, Yuval
;
• Cirelli, Chiara
;
• Tononi, Giulio

Abstract

In an awake state, neurons in the cerebral cortex fire irregularly and electroencephalogram (EEG) recordings display low-amplitude, high-frequency fluctuations. During sleep, neurons oscillate between `on' periods, when they fire as in an awake brain, and `off' periods, when they stop firing altogether and the EEG displays high-amplitude slow waves. However, what happens to neuronal firing after a long period of being awake is not known. Here we show that in freely behaving rats after a long period in an awake state, cortical neurons can go briefly `offline' as in sleep, accompanied by slow waves in the local EEG. Neurons often go offline in one cortical area but not in another, and during these periods of `local sleep', the incidence of which increases with the duration of the awake state, rats are active and display an `awake' EEG. However, they are progressively impaired in a sugar pellet reaching task. Thus, although both the EEG and behaviour indicate wakefulness, local populations of neurons in the cortex may be falling asleep, with negative consequences for performance.