Spontaneous thoughts and experiences across wakefulness and sleep

Consciousness research is commonly divided into two main areas: the study of states of consciousness and the study of contents of consciousness. States of consciousness refer to discrete modes of awareness elicited by normal states of the brain, such as those associated with wakefulness and sleep, and by abnormal factors, including brain lesions, pharmacological agents and other external interventions. Contents of consciousness refer what we are conscious of. In this chapter, we emphasize the dynamic nature of consciousness in terms of both its states and contents. First, we first observe that our life constantly alternates between different conscious and unconscious states, namely, sleep and wakefulness. Then, within each state, we note an inherent dynamism in content, with conscious experience ranging from content-full to content-less. By surveying the variety of conscious experiences across wakefulness and sleep, we highlight the similarities in reported contents across these states. We further discuss how the possibility of having conscious experiences without specific content challenges the idea that being conscious necessarily involves being conscious of something. Finally, by reviewing the literature on the neural correlates of consciousness, we propose a potential convergence in the study of conscious states and contents.