In humans, REM sleep behaviour disorders that are a consequence of dysfunctions of the balance between endogenous activation and inhibition come in different degrees of severity. This chapter reviews evidence pertaining to the neural basis of state and trait consciousness. It discusses sleep as an example of circadian endogenous state changes; general anaesthesia as an example of chemically induced state changes; and comatose, vegetative, and minimally conscious states as examples of pathology-induced state changes. Both attention and the conscious access to the information that is required for the subjects to be able to communicate that they have a conscious representation of the information invoke frontoparietal cortices. The neural correlates of conscious sensations and representations depend on many factors. The functional neuroanatomy of sleep provides experimental support, as both REM and non-REM sleep are characterized by a decrease in frontoparietal activation, although extended periods of sleep brim with phenomenal experiences.