Distinguishing cortical indexes of arousal and awareness in sleeping patients with unresponsive wakefulness syndrome

Consciousness is assumed to be defined by two components: awareness and arousal. However, the cortical indexes for these two components remain unclear. Since patients with unresponsive wakefulness syndrome (UWS) are supposed to have no awareness but arousal, sleep-wake cycle in patients with UWS may reflect pure arousal fluctuations, and then could distinguish the cortical indexes for arousal from ones for awareness. This study recorded nighttime polysomnography in patients with UWS, patients with minimally conscious state (MCS) and healthy controls, showing that spectral slope could index arousal, fluctuating among sleep stages in all three groups. Both spectral entropy and Lempel-Ziv complexity can index awareness, showing a significant difference between conscious and unconscious states. These findings provide fundamental evidence for the two-component hypothesis of consciousness.