Large-scale signatures of unconsciousness are consistent with a departure from critical dynamics

Abstract

Loss of cortical integration and changes in the dynamics of electrophysiological brain signals characterize the transition from wakefulness towards unconsciousness. In this study, we arrive at a basic model explaining these observations based on the theory of phase transitions in complex systems. We studied the link between spatial and temporal correlations of large-scale brain activity recorded with functional magnetic resonance imaging during wakefulness, propofol-induced sedation and loss of consciousness and during the subsequent recovery. We observed that during unconsciousness activity in frontothalamic regions exhibited a reduction of long-range temporal correlations and a departure of functional connectivity from anatomical constraints. A model of a system exhibiting a phase transition reproduced our findings, as well as the diminished sensitivity of the cortex to external perturbations during unconsciousness. This framework unifies different observations about brain activity during unconsciousness and predicts that the principles we identified are universal and independent from its causes.

Microscopic Engine Powered by Critical Demixing

“…molecular motors acting within a cellular membrane). Considering the wide range of systems that can be tuned near criticality, we can exploit any other order parameter tuned near criticality in a given system, such as pH-value and particle concentration [29]. Since phase separations have been already widely found inside the human body [16,17] and some of them are known to be sources of diseases such as protein condensations [18], new biocompatible engines can be designed based on our critical engine that could be able to perform medical surgeries non-invasively such as the treatment of arteriosclerosis.…”

Self‐Organized Temporal Criticality: Bottom‐Up Resilience versus Top‐Down Vulnerability

“…In the case of the brain dynamics there is wide consensus on the connection between consciousness and criticality. See, for instance, [9,[16][17][18] and the recent review paper [19]. The electroencephalogram (EEG) signals are characterized by abrupt changes, called rapid transition processes (RTP), which are proved [20,21] to be renewal non-Poisson events, with ≈ 2.…”

“…The value of adjusts according to (11) from small values around 0.2 to a maximal value of 1.8, which is known to correspond to a supercritical condition in the case of the conventional DMM. When using the fine tuning control parameter approach we set = 1.8; the social system is far from the intelligence condition that according to a widely accepted opinion [9,[16][17][18][19]] requires criticality. (11) for the same regular two-dimensional network of Figure 1; red line: the time evolution of ( ) of the self-organized system described by the black under the influence of the weak noisy perturbation described in Section 4.…”

Exploring the Computational Explanatory Gap

“…The terms local and global, when applied to neurocognitive architectures, generally refer to the spatial extent of information processing. A number of empirical studies have suggested that information processing during conscious mental activities is widely distributed ("global") across cerebral cortex regions and also associated with increased inter-regional communication [42][43][44]. Inspired by this, a number of neural network models have been studied in which conscious/effortful information processing is associated with computational processes involving the recruitment of hidden layers and hence widespread network activation of a "global workspace" [45,46].…”