Normal Sleep EEG

The electroencephalogram (EEG) is the fundamental and most common tool used in sleep research. Normal human sleep comprises two states—rapid eye movement (REM) and non-REM (NREM) sleep—that alternate cyclically across the night. Each state presents typical features that can be detected by EEG and polygraphic channels: NREM sleep includes synchronous cortical electroencephalogram elements (sleep spindles, K-complexes, and slow waves) associated with low muscle tonus; in REM sleep, EEG is desynchronized, muscles are atonic, and dreaming is typically reported. A clear appreciation of the physiological characteristics of sleep provides a strong background for understanding clinical conditions in which “normal” characteristics are altered. The goal of this chapter is to define and describe the EEG-based recognizable elements of physiological sleep in humans, with attention to their clinical implications and their significance for better understanding the underlying cerebral mechanisms. Updated theories of sleep features, function and underlying brain circuits are discussed based on advanced neurophysiological techniques. We focus to the normal EEG sleep pattern in young adults as a working baseline pattern. However, normative changes due to aging and other factors are described.