Consciousness consists of two components: arousal (wakefulness or level of consciousness) and awareness (contents of consciousness) (1). RESULTS CONCLUSIONPreliminary results indicate that the complexity of sleep is higher in MCS than VS patients. Especially, sleep features such as REM sleep, SWS, and sleep spindles as well as cortical desynchronization arousals appear to distinguish between the two clinical entities.It is suggested that this "complexity" of residual sleep patterns reflects more intact thalamo-cortically connected brains. Yet, results are to be interpreted with caution as classical R & K criteria are hard to apply in this DOC population. Especially, the general slowing of EEG frequencies make reliable SWS or spindle detection impossible. We therefore also consider more quantiative sleep analysis as depicted in Fig. 3-4.Overall it is suggested that clinical diagnosis as well as prognosis of DOC patients can be refined using 24hr PSG recordings.