Journal of Cognitive Neuroscience
June 1, 2010
Audrey Vanhaudenhuyse, Athena Demertzi, Manuel Schabus et al.
460 citations
Resting brain activity reveals two anticorrelated cortical systems linked to conscious awareness: an extrinsic system (lateral fronto-parietal areas) associated with external awareness and an intrinsic system (medial brain areas) associated with internal awareness. In 31 healthy volunteers, external and internal awareness were significantly anticorrelated, with a mean switching frequency of 0.05 Hz, similar to BOLD fMRI slow oscillations. In 22 volunteers, fMRI showed that precuneus/posterior cingulate, anterior cingulate/mesiofrontal cortices, and parahippocampal areas (intrinsic system) correlated with internal awareness, while lateral fronto-parietal cortices (extrinsic system) correlated with external awareness.
Anesthesiology
August 9, 2016
Vincent Bonhomme, Audrey Vanhaudenhuyse, Athena Demertzi et al.
206 citations
Ketamine alters consciousness by disrupting connectivity within and between specific resting-state brain networks, particularly the default mode network (DMn) and salience network (SALn), while leaving sensory and motor networks largely intact. In healthy volunteers given stepwise ketamine infusions until they lost responsiveness, DMn connectivity between the medial prefrontal cortex and other network regions decreased (from 0.20 to 0.07), and the normal anticorrelated activity between the DMn and sensory regions reversed (e.g., right sensory cortex shifted from -0.07 to 0.04). SALn connectivity was also suppressed but nonuniformly. These specific changes, including preserved sensory network connectivity, are shared with propofol-induced unconsciousness.
Communications Biology
July 5, 2023
Idan E Nemirovsky, Nicholas J M Popiel, Jorge Rudas et al.
Integrated Information Theory aims to explain and measure consciousness by quantifying how integrated a system's causal properties are. This work implemented version 3.0 of the theory on functional MRI data from 17 healthy volunteers sedated with propofol. Using the PyPhi software, the measure Φmax was computed and compared with other proposed consciousness metrics: an earlier integrated information version, Granger causality, and correlation-based functional connectivity. Φmax showed varied responses to sedation across different brain networks. Changes in Φmax closely tracked changes in conscious level within the frontoparietal and dorsal attention networks, which support higher-order cognition. The findings offer guidance for future use of these measures in neuroimaging.
Entropy (Basel, Switzerland)
March 16, 2020
Nicholas J M Popiel, Sina Khajehabdollahi, Pubuditha M. Abeyasinghe et al.
Integrated information, a measure proposed by Integrated Information Theory as a correlate of conscious experience, behaves as an order parameter that undergoes a phase transition at the critical point in generalized Ising models of small neural networks. In simulations of 159 random, positively weighted five-node excitatory networks, integrated information peaked at the critical temperature, where its generalized susceptibility was maximal. At this point, the system was maximally receptive and responsive to perturbations of its own states. The findings show that integrated information can capture critical behavior in an empirical dataset derived from the generalized Ising model.
bioRxiv Preprint Server
January 15, 2019
Sina Khajehabdollahi, Pubuditha M. Abeyasinghe, Adrian M. Owen et al.
preprint
Using the critical Ising model of the brain, integrated information—a measure of consciousness—was measured in toy models of generic neural networks. Monte Carlo simulations were run on 159 random weighted networks analogous to small 5-node neural network motifs. Integrated information, as a type of order parameter like magnetism, undergoes a phase transition at the model's critical point, where the system's 'consciousness' is maximally susceptible to perturbations and on the boundary between ordered and disordered forms. This adds evidence that the emergence of consciousness coincides with self-organized criticality, evolution, the emergence of complexity, and the integration of complex systems.
Functional MRI
December 1, 2018
Nasim Mortazavi, Cécile Staquet, Audrey Vanhaudenhuyse et al.
Hypnotic anesthetic agents dose-dependently alter brain resting-state networks (RSNs) that sustain consciousness, with each agent producing distinct, non-uniform effects within a network that likely correspond to the clinical features observed during their use. Observations during anesthesia help link RSNs to specific aspects of consciousness and environmental connectedness, though the precise connection to biochemical targets or sleep-wake regulation remains unclear. PET studies using targeted radiolabeled probes offer insights, and advanced analytical methods like Granger causality may further clarify brain region interactions. The hypnotic state, useful for surgery without general anesthesia, produces specific RSN changes that distinguish it from normal wakefulness and anesthesia.