Complexity of Multi-Dimensional Spontaneous EEG Decreases during Propofol Induced General Anaesthesia

PLoS One. 2015 Aug 7;10(8):e0133532. doi: 10.1371/journal.pone.0133532. eCollection 2015.


Emerging neural theories of consciousness suggest a correlation between a specific type of neural dynamical complexity and the level of consciousness: When awake and aware, causal interactions between brain regions are both integrated (all regions are to a certain extent connected) and differentiated (there is inhomogeneity and variety in the interactions). In support of this, recent work by Casali et al (2013) has shown that Lempel-Ziv complexity correlates strongly with conscious level, when computed on the EEG response to transcranial magnetic stimulation. Here we investigated complexity of spontaneous high-density EEG data during propofol-induced general anaesthesia. We consider three distinct measures: (i) Lempel-Ziv complexity, which is derived from how compressible the data are; (ii) amplitude coalition entropy, which measures the variability in the constitution of the set of active channels; and (iii) the novel synchrony coalition entropy (SCE), which measures the variability in the constitution of the set of synchronous channels. After some simulations on Kuramoto oscillator models which demonstrate that these measures capture distinct 'flavours' of complexity, we show that there is a robustly measurable decrease in the complexity of spontaneous EEG during general anaesthesia.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anesthesia, General*
  • Area Under Curve
  • Cerebral Cortex / physiology
  • Computer Simulation
  • Electrodes
  • Electroencephalography / methods*
  • Entropy
  • Humans
  • Models, Theoretical
  • Propofol / pharmacology*
  • ROC Curve
  • Time Factors


  • Propofol

Grants and funding

MMS is supported by a GTA of the Department of Informatics, University of Sussex. ABB is supported by Engineering and Physical Sciences Research Council fellowship EP/L005131/1. AKS is supported from The Dr. Mortimer and Theresa Sackler Foundation, as part of their support of the Sackler Centre for Consciousness Science. SL is a Belgian Funds for Scientific Research (FRS) Senior Research Associate and MAB, QN and MB are FRS Postdoctoral Researchers. This work was also supported by the European Commission (DECODER), Fondazione Europea di Ricerca Biomedica, McDonnell Foundation, Mind Science Foundation, Public Utility Foundation ‘‘Université Européenne du Travail’’ and the University of Liège. Possible inaccuracies of information are the responsibility of the project team. The text reflects solely the views of its authors. The European Commission is not liable for any use that may be made of the information contained herein. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.