Understanding Sleep
Sleep Architecture
Profile of a normal sleep cycle
A normal human sleep pattern consists of five successive stages that together form the sleep cycle, and usually represented as a hypnogram (Figure 1). The five stages are grouped according to the rate of eye movement during the sleep stage – non-rapid eye movement (NREM) and rapid eye movement (REM). NREM sleep is further categorised into light NREM sleep (Stages 1 and 2) and deep NREM sleep (Stages 3 and 4). Stages 3 and 4 of NREM sleep are also referred to as slow wave sleep (SWS).1 These sleep cycle stages are described in more detail within the 'sleep cycle stages' section.
References:
1. Bae CJ, Foldvary-Schaefer N. Normal human sleep. In: Carney PR, Berry RB, Geyer JD, eds. Clinical Sleep Disorders. © Lippincott Williams & Wilkins, Philadelphia, USA, 2005: 29–37.
2. Rechtschaffen A, Siegel, J. Sleep and dreaming. In: Principles of neuroscience. Fourth Edition. Kandal ER, Schwartz JH, Jessell TM, eds. © McGraw-Hill Companies, Inc. USA. 2000; p936–947.