Spontaneous nystagmus across the sleep-wake cycle in vegetative state patients.

The presence of spontaneous CNS nystagmus during wakefulness was documented for the first time in 6 vegetative-state (VS) patients. Nystagmus of smaller amplitude as compared to the awake state was consistently detected in each patient during stage 1 of sleep. There was complete absence of nystagmus during stage 2 and slow wave sleep (SWS) in all the patients. Clear nystagmus episodes were observed during rapid eye movement (REM) sleep in all patients. Some nystagmus episodes followed rapid eye movements (REMs), some were unrelated to REMs while others were superimposed on REMs. It is suggested that spontaneous neural activation during REM sleep may allow the episodic emergence of nystagmus during this sleep stage.