Cyclic alternating pattern

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The cyclic alternating pattern (abbreviated CAP) is a pattern of two, long-lasting alternate electroencephalogram (EEG) patterns that occur in sleep, as described by Terzano, et al., in 1985.[1] It is a pattern of spontaneous cortical activity,[2] which is ongoing and in the absence of sensory stimulation. It is the reorganization of the sleeping brain challenged by the modification of environmental conditions and it is characterized by periodic abnormal electrocortical activity that recurs with a frequency of up to one minute.[3] It is considered "the EEG marker of unstable sleep".[4] CAP does not occur during REM. In Lennox-Gastaut syndrome, CAP modulates the occurrence of clinical seizures and generalized epileptic discharges by means of a gate-control mechanism.[5]

CAP is a marker of sleep instability and it is found during non-rapid eye movement sleep. CAP is organized into sequences of successive cycles composed of two phases, A and B. Phase A involves phasic events, in other words, not continuous. Phase A subtypes of CAP allow adaptive adjustments of ongoing states to internal and external inputs.[6] Phase B refers to background rhythm during CAP. Furthermore, CAP involves cerebral activities and is influenced by autonomic and motor functions. Interaction between CAP and neurovegetative fluctuations and motor events determine the pathophysiology of several sleep disorders and the effect of medication on continuous positive airway pressure (CPAP) treatment (CPAP is used to treat obstructive sleep apnea or OSA).[7]

CAP is a marker of NREM instability and is also the "master clock" that accompanies the stage transitions maintained in sleep phases, noted in both the EEG and by autonomic functions through regular fluctuations. CAP is decreased in narcolepsy, multiple system atrophy, in certain cases of drug administration, with CPAP treatment for OSA, and during night-time recovery sleep after prolonged sleep deprivation.[6] There is a relationship present between CAP and arousals that allows for adjustments of vigilance during sleep. If there is a failure in this relationship during sleep, sleep disorders may develop.

Rechtschaffen and Kales developed the standard criteria for sleep staging in 1968.[8] In 1992, the AASM defined arousals as markers of sleep disruption, which is harmful for sleep. According to Boselli, et al., in 1998 it was noted that spontaneous arousals are natural in sleep and increase over life.[9]


  1. ^ Terzano, M. G.; Mancia, D.; Salati, M. R.; Costani, G.; Decembrino, A.; Parrino, L. (1985). "The cyclic alternating pattern as a physiologic component of normal NREM sleep". Sleep. 8 (2): 137–145. doi:10.1093/sleep/8.2.137. ISSN 0161-8105. PMID 4012156.
  2. ^ Kryger (2017). Principles and Practice of Sleep Medicine. Elsevier. p. 1576. ISBN 9780323242882.
  3. ^ Parrino, Liborio; Grassi, Andrea; Milioli, Giulia (November 2014). "Cyclic alternating pattern in polysomnography: what is it and what does it mean?". Current Opinion in Pulmonary Medicine. 20 (6): 533–541. doi:10.1097/MCP.0000000000000100. ISSN 1531-6971. PMID 25188718.
  4. ^ Parrino, Liborio; Ferri, Raffaele; Bruni, Oliviero; Terzano, Mario G. (February 2012). "Cyclic alternating pattern (CAP): the marker of sleep instability". Sleep Medicine Reviews. 16 (1): 27–45. doi:10.1016/j.smrv.2011.02.003. ISSN 1532-2955. PMID 21616693.
  5. ^ Eisensehr, I.; Parrino, L.; Noachtar, S.; Smerieri, A.; Terzano, M.G. (2001-09-01). "Sleep in Lennox–Gastaut syndrome: the role oft the cyclic alternating pattern (CAP) in the gate control of clinical seizures and generalized polyspikes". Epilepsy Research. 46 (3): 241–250. doi:10.1016/S0920-1211(01)00280-7. ISSN 0920-1211. PMID 11518625.
  6. ^ a b Kryger (2017). Principles and Practice of Sleep Medicine. Elsevier. pp. 1586–1587. ISBN 9780323242882.
  7. ^ "Cyclic alternating pattern". Retrieved 2018-11-08.
  8. ^ "A manual of standardized terminology, techniques and scoring system for sleep stages of human subjects. Allan Rechtschaffen and Anthony Kales, editors. - NLM Catalog - NCBI". Retrieved 2018-11-08.
  9. ^ Boselli, M.; Parrino, L.; Smerieri, A.; Terzano, M. G. (1998-06-15). "Effect of age on EEG arousals in normal sleep". Sleep. 21 (4): 351–357. ISSN 0161-8105. PMID 9646379.