Sleep and Consciousness

Abstract

Sleep offers a unique opportunity to relate changes in brain activity to changes in consciousness. Indeed, if it were not for sleep, when consciousness fades in and out on a regular basis, it might be hard to imagine that consciousness is not a given but depends somehow on the way our brain is functioning. At the same time as changes in consciousness occur, brain activity undergoes major changes through an orderly progression of sleep stages, which can be identified by recording the electroencephalogram (EEG), eye movements (EOG), and muscle tone (EMG). Within each sleep stage, there are frequent, short-lasting electrophysiological phenomena, such as slow oscillations and spindles representing moments at which brain activity undergoes important fluctuations. There are also orderly spatial changes in the activation of many brain regions, as indicated by imaging studies. Importantly, similar brain activities occur in animals, and this has spearheaded detailed studies of the underlying neural mechanisms.