| Common categorizations of consciousness distinguish between basal and higher-order aspects of this multifaceted concept. Basal consciousness comprises perceptions and sensations, whereas higher-order consciousness constitutes reflections on these perceptions. In rapid eye movement (REM) sleep, ordinary dreaming comprises only basal aspects of consciousness. There is conscious perception of dream content but higher-order aspects of consciousness are usually absent: The person does not realize that he is dreaming and has no perception of the self as an agent endowed with intentionality and free will. Higher-order consciousness therefore seems to be bound to wakefulness. However, a special type of dreaming - referred to as "lucid dreaming" - is characterized by full-blown consciousness, including all higher-order aspects: The dreamer is able to reflect on his state of consciousness and realizes that he is dreaming. Using a combined fMRI/EEG approach, we could reveal neural activity related to the genesis of higher-order consciousness by contrasting ordinary REM sleep with physiologically verified lucid REM sleep. We find increased activation in a range of neo-cortical regions, including bilateral precuneus, cuneus and parietal, prefrontal and occipito-temporal cortices, to be related to this categorical shift in consciousness. This activation shows remarkable overlap with neo-cortical regions that have highest expansion in humans relative to non-human primates. |
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