Sleep patterns open the window into disorders of consciousness

The presence of sleep-wakefulness cycles is one of the main clinical symptoms marking the transition from coma to chronic disorders of consciousness (DoC). That is, eyes of coma patients are regularly closed while eyes of DoC patients are sometimes closed, sometimes opened. But does it mean that they really sleep? Landsness et al. (2011) published a broadly cited study in which they reported that only one group of DoC patients (those with the diagnosis of Minimally Conscious State, or MCS: Giacino et al., 2002) slept in the exact physiological sense of this term, i.e., they had regular circadian changes of EEG, electrooculogram (EOG), and muscle tone similar (though not identical) to those of healthy humans.

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