Cortical Blinks (microsleep) occur during wakefulness affecting behavior

Local sleep in awake rats

Vladyslav V. Vyazovskiy, Umberto Olcese, Erin C. Hanlon, Yuval Nir, Chiara Cirelli & Giulio Tononi
AffiliationsContributionsCorresponding author
Nature 472, 443–447 (28 April 2011) doi:10.1038/nature10009
Received 30 August 2010 Accepted 17 March 2011 Published online 27 April 2011

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.

[The rats were awake, but awake with a nice sprinkling of localized sleep in the cortex,” says Guilio Tononi, a neuroscientist at the University of Wisconsin–Madison and lead author of the study.]

[By recording the activity of many small populations of neurons, Tononi and his colleagues showed that OFF states occur randomly throughout the cortex when a rat has been awake for a long time. “If we could watch the whole brain, it would be like watching boiling water – when you are awake, just before boiling, all the neurons are ON. As the animal gets tired, the OFF periods would then be the bubbles; where they appear is impossible to predict,” he says.]

[Slow waves were thought to be absent during normal waking behaviour, but the new study emphasizes that slow-wave activity can be very localized, says David McCormick, a neurobiologist at Yale University in New Haven, Connecticut. “Call it a cortical blink — just a brief shutdown of a piece of cortex that can disrupt neural processing.”]


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