Approximate Entropy in the Electroencephalogram during Wake and Sleep

Naoto Burioka, Masanori Miyata, Germaine G Cornelissen-Guillaume, Franz Halberg, Takao Takeshima, Daniel T. Kaplan, Hisashi Suyama, Masanori Endo, Yoshihiro Maegaki, Takashi Nomura, Yutaka Tomita, Kenji Nakashima, Eiji Shimizu

Research output: Contribution to journalArticlepeer-review

131 Scopus citations


Entropy measurement can discriminate among complex systems, including deterministic, stochastic and composite systems. We evaluated the changes of approximate entropy (ApEn) in signals of the electroencephalogram (EEG) during sleep. EEG signals were recorded from eight healthy volunteers during nightly sleep. We estimated the values of ApEn in EEG signals in each sleep stage. The ApEn values for EEG signals (mean ± SD) were 0.896 ± 0.264 during eyes-closed waking state, 0.738 ± 0.089 during Stage I, 0.615 ± 0.107 during Stage II, 0.487 ± 0.101 during Stage III, 0.397 ± 0.078 during Stage IV and 0.789 ± 0.182 during REM sleep. The ApEn values were found to differ with statistical significance among the six different stages of consciousness (ANOVA, p<0.001). ApEn of EEG was statistically significantly lower during Stage IV and higher during wake and REM sleep. We conclude that ApEn measurement can be useful to estimate sleep stages and the complexity in brain activity.

Original languageEnglish (US)
Pages (from-to)21-24
Number of pages4
JournalClinical EEG and Neuroscience
Issue number1
StatePublished - Jan 2005

Bibliographical note

Funding Information:
This study was partly supported by a grant (11-KOU-179) from the Ministry of Education, Science, Sports and Culture, Japan.


  • Approximate
  • Electroencephalography
  • Entropy
  • Key Words
  • Nonlinear Analysis
  • Sleep Stage
  • System Complexity


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