You are in: eMedicine Specialties > Neurology > EEG Atlas: Normal Sleep EEG - Stage IIArticle Last Updated: *ba 0, 0AUTHOR AND EDITOR INFORMATIONSection 1 of 6
  Author: Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital Selim R Benbadis is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association Coauthor(s): Diego Rielo, MD, Staff Physician, Department of Neurology, Memorial Hospital West, Memorial Hospital Pembroke, Memorial Healthcare Editors: Leslie Huszar, MD, Consulting Staff, Department of Neurology, Indian River Memorial Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital; Paul E Barkhaus, MD, Professor, Department of Neurology, Medical College of Wisconsin; Director of Neuromuscular Diseases, Milwaukee Veterans Administration Medical Center; Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants Author and Editor Disclosure Synonyms and related keywords: EEG atlas, normal sleep EEG, stage II sleep, K complex, sleep spindle, sleep stages, rapid eye movement sleep, REM sleep, nonrapid eye movement sleep, NREM sleep, stage II waveforms INTRODUCTIONSection 2 of 6
  Loomis provided the earliest detailed description of various stages of sleep in the mid 1930s, and in the early 1950s Aserinsky and Kleitman identified rapid eye movement (REM) sleep. Sleep generally is divided in two broad types: nonrapid eye movement (NREM) sleep and REM sleep. On the basis of EEG changes, NREM is divided further into 4 stages (stage I, stage II, stage III, stage IV). NREM and REM occur in alternating cycles, each lasting approximately 90-100 minutes, with a total of 4-6 cycles. In general, in the healthy young adult NREM sleep accounts for 75-90% of sleep time (3-5% stage I, 50-60% stage II, and 10-20% stages III and IV). REM sleep accounts for 10-25% of sleep time. Stage II is the predominant sleep stage during a normal night's sleep. The distinct and principal EEG criterion to establish stage II sleep is the appearance of sleep spindles or K complexes. The presence of sleep spindles is necessary and sufficient to define stage II sleep. Another characteristic finding of stage II sleep is the appearance of K complexes, but since K complexes typically are associated with a spindle, spindles are the defining features of stage II sleep. Except for slow rolling eye movements, all patterns described under stage I persist in stage II sleep (see EEG Atlas: Normal Sleep EEG – Stage I). Representative examples of the waveforms described here are shown in Images 1-6. Patient Education For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education articles Sleep: Understanding the Basics and Electroencephalography (EEG). WAVEFORM DESCRIPTIONSSection 3 of 6
Sleep spindles normally first appear in infants aged 6-8 weeks and are bilaterally asynchronous. These become well-formed spindles and bilaterally synchronous by the time the individual is aged 2 years. Sleep spindles have a frequency of 12-16 Hz (typically 14 Hz) and are maximal in the central region (vertex), although they occasionally predominate in the frontal regions. They occur in short bursts of waxing and waning spindlelike (fusiform) rhythmic activity. Amplitude is usually 20-100 µV. Extreme spindles (described by Gibbs and Gibbs) are unusually high-voltage (100-400 µV) and prolonged (>20 s) spindles located over the frontal regions. K complexes (initially described by Loomis) are high amplitude (>100 µV), broad (>200 ms), diphasic, and transient and often are associated with sleep spindles. Location is frontocentral, with a typical maximum at the midline (central midline placement of electrodes [Cz] or frontal midline placement of electrodes [Fz]). They occur spontaneously and are elicited as an arousal response. They may have an association with blood pressure fluctuation during sleep. CLINICAL CORRELATIONSection 4 of 6
The stigmata of stage II sleep, spindles and K complexes, are usually easy to identify and are less subject to overinterpretation or misinterpretation than the patterns of stage I sleep. MULTIMEDIASection 5 of 6
REFERENCESSection 6 of 6
EEG Atlas: Normal Sleep EEG - Stage II excerpt Article Last Updated: *ba 0, 0 | ||||||||||||||||||||||||||||||||||||||||||
