Brain Networks Maintain a Scale-free Organization across Consciousness, Anesthesia, and Recovery

Abstract

Background:Loss of consciousness is an essential feature of general anesthesia. Although alterations of neural networks during anesthesia have been identified in the spatial domain, there has been relatively little study of temporal organization. Methods: Ten healthy male volunteers were anesthetized with an induction dose of propofol on two separate occasions. The duration of network connections in the brain was analyzed by multichannel electroencephalography and the minimum spanning tree method. Entropy of the connections was calculated based on Shannon entropy. The global temporal configuration of networks was investigated by constructing the cumulative distribution function of connection times in different frequency bands and different states of consciousness. Results: General anesthesia was associated with a significant reduction in the number of network connections, as well as significant alterations of their duration. These changes were most prominent in the ␦ bandwidth and were also associated with a significant reduction in entropy of the connection matrix. Despite these and other changes, a global "scale-free" organization was consistently preserved across multiple subjects, anesthetic exposures, states of consciousness, and electroencephalogram frequencies. Conclusions: Our data suggest a fundamental principle of temporal organization of network connectivity that is maintained during consciousness and anesthesia, despite local changes. These findings are consistent with a process of adaptive reconfiguration during general anesthesia.

The trees and the forest: Characterization of complex brain networks with minimum spanning trees

“…No differences in degree distribution were found between the three groups. Ciftçi (2011) noted a distinction between highly persistant and less consistent edges, somewhat in line with the results of Lee et al (Lee et al, 2010). Hierarchical clustering analysis of the MST showed that the connection between the hippocampus/parahippocampal gyrus on the one hand to the precuneus and posterior cingulate gyrus on the other hand, that is normally mediated by the angular gyrus and the inferior temporal gyrus, was disrupted in Alzheimer patients.…”

“…The distribution of connection survival times showed a power law, but did not change during the three different states, which was interpreted as reflecting adaptive reconfiguration of functional brain networks. Of particular interest, as can be seen in Fig.3 in (Lee et al, 2010), a subgroup of connections was much more stable over time. This subset could correspond to a stable backbone, and perhaps to the superhighways reported in theoretical work (Wu et al, 2006).…”

“…One problem with this study is that results in the gamma band derived from scalp EEG may be severely affected by muscle artefact (Whitham et al, 2007). Of note, this was explicitly considered in the study of Lee et al (2010) where the gamma band was left out of the analysis.…”

“…The same group applied a slightly modified version of the MST EEG analysis in a later study concerning network changes in states of altered consciousness (Lee et al, 2010). Ten healthy male volunteers were investigated before, during and after Propofol-induced anesthesia.…”

Spatiotemporal Reconfiguration of Large-Scale Brain Functional Networks during Propofol-Induced Loss of Consciousness

“…A relative maintenance of global principles may reflect an adaptive reconfiguration of brain organization , a process that has also been suggested for propofol-induced transitions of consciousness in a recent EEG study (Lee et al, 2010). A significant increase in values of the clustering ratio ␥ was found during PI-LOC compared with wakefulness.…”