Abstract
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.
Highlights
The idea that the level and range of consciousness relates in some way to dynamical complexity of brain activity is becoming increasingly prominent [1,2,3,4,5,6,7]
A common way to conceptualize dynamical complexity in this setting is as simultaneous differentiation and integration, and this idea draws from what is taken to be a fundamental property of conscious experience, namely that each conscious scene is composed of many different parts and is different from every other conscious scene, yet each conscious scene is experienced as a PLOS ONE | DOI:10.1371/journal.pone
These two different analysis show respectively: (i) each measure captures the degree of randomness in binary matrices of activations (LZc, amplitude coalition entropy (ACE)) or synchronies (SCE); (ii) there exists a scenario in which synchrony coalition entropy (SCE) diverges from Lempel-Ziv complexity (LZc) and ACE and captures a distinct ‘flavour’ of complexity
Summary
The idea that the level and range of consciousness relates in some way to dynamical complexity of brain activity is becoming increasingly prominent [1,2,3,4,5,6,7]. A common way to conceptualize dynamical complexity in this setting is as simultaneous differentiation (subsets of the system being dynamically distinct) and integration (the system as a whole exhibiting coherence), and this idea draws from what is taken to be a fundamental property of conscious experience, namely that each conscious scene is composed of many different parts and is different from every other conscious scene (differentiation), yet each conscious scene is experienced as a PLOS ONE | DOI:10.1371/journal.pone.0133532. Sackler Foundation, as part of their support of the Sackler Centre for Consciousness Science. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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