title: Loss of Consciousness Is Associated with Stabilization of Cortical Activity.
abstract: What aspects of neuronal activity distinguish the conscious from the unconscious brain? This has been a subject of intense interest and debate since the early days of neurophysiology. However, as any practicing anesthesiologist can attest, it is currently not possible to reliably distinguish a conscious state from an unconscious one on the basis of brain activity. Here we approach this problem from the perspective of dynamical systems theory. We argue that the brain, as a dynamical system, is self-regulated at the boundary between stable and unstable regimes, allowing it in particular to maintain high susceptibility to stimuli. To test this hypothesis, we performed stability analysis of high-density electrocorticography recordings covering an entire cerebral hemisphere in monkeys during reversible loss of consciousness. We show that, during loss of consciousness, the number of eigenmodes at the edge of instability decreases smoothly, independently of the type of anesthetic and specific features of brain activity. The eigenmodes drift back toward the unstable line during recovery of consciousness. Furthermore, we show that stability is an emergent phenomenon dependent on the correlations among activity in different cortical regions rather than signals taken in isolation. These findings support the conclusion that dynamics at the edge of instability are essential for maintaining consciousness and provide a novel and principled measure that distinguishes between the conscious and the unconscious brain.
  
  
  CONCLUSIONS
  What distinguishes brain activity during consciousness from that observed during unconsciousness? Answering this question has proven difficult because neither consciousness nor lack thereof have universal signatures in terms of most specific features of brain activity. For instance, different anesthetics induce different patterns of brain activity. We demonstrate that loss of consciousness is universally and reliably associated with stabilization of cortical dynamics regardless of the specific activity characteristics. To give an analogy, our analysis suggests that loss of consciousness is akin to depressing the damper pedal on the piano, which makes the sounds dissipate quicker regardless of the specific melody being played. This approach may prove useful in detecting consciousness on the basis of brain activity under anesthesia and other settings.
authors.affiliation: Laboratories of Mathematical Physics and Integrative Neuroscience Laboratory, Buenos Aires, Argentina, Instituto de Cálculo, Faculty of Natural Sciences, University of Buenos Aires (C1428EGA), Buenos Aires, Argentina.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Solovey
authors.affiliation: Laboratories of Mathematical Physics and.
authors.forename: Leandro M
authors.initials: LM
authors.lastname: Alonso
authors.affiliation: Laboratory for Adaptive Intelligence, Brain Science Institute, RIKEN, Saitama, 351-0198 Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Yanagawa
authors.affiliation: Laboratory for Adaptive Intelligence, Brain Science Institute, RIKEN, Saitama, 351-0198 Japan.
authors.forename: Naotaka
authors.initials: N
authors.lastname: Fujii
authors.affiliation: Laboratories of Mathematical Physics and.
authors.forename: Marcelo O
authors.initials: MO
authors.lastname: Magnasco
authors.affiliation: Computational Biology Center, T. J. Watson IBM Research Laboratory, Yorktown Heights, New York 10598, and.
authors.forename: Guillermo A
authors.initials: GA
authors.lastname: Cecchi
authors.affiliation: Neurobiology and Behavior, Rockefeller University, New York, New York 10065, Department of Anesthesiology, Weill Medical Center, New York, New York 10065 proekt@gmail.com.
authors.forename: Alex
authors.identifier: http://orcid.org/0000-0002-9272-5337
authors.initials: A
authors.lastname: Proekt
mesh_terms: D000777:Anesthetics / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D003243:Consciousness / Q000187:drug effects / Q000502:physiology*; D004569:Electroencephalography; D000882:Haplorhini; D008297:Male; D012815:Signal Processing, Computer-Assisted; D014474:Unconsciousness
chemical_list: D000777:Anesthetics
keywords: ECoG; anesthesia; consciousness; dynamical criticality; dynamical systems; stability analysis