title: Modelling general anaesthesia as a first-order phase transition in the cortex.
abstract: Since 1997 we have been developing a theoretical foundation for general anaesthesia. We have been able to demonstrate that the abrupt change in brain state brought on by anaesthetic drugs can be characterized as a first-order phase transition in the population-average membrane voltage of the cortical neurons. The theory predicts that, as the critical point of phase change into unconsciousness is approached, the electrical fluctuations in cortical activity will grow strongly in amplitude while slowing in frequency, becoming more correlated both in time and in space. Thus the bio-electrical change of brain-state has deep similarities with thermodynamic phase changes of classical physics. The theory further predicts the existence of a second critical point, hysteretically separated from the first, corresponding to the return path from comatose unconsciousness back to normal responsiveness. There is a steadily accumulating body of clinical evidence in support of all of the phase-transition predictions: low-frequency power surge in EEG activity; increased correlation time and correlation length in EEG fluctuations; hysteresis separation, with respect to drug concentration, between the point of induction and the point of emergence.
authors.affiliation: Department of Physics and Electronic Engineering, University of Waikato, Private Bag 3105, Hamilton, New Zealand. msr@phys.waikato.ac.nz
authors.forename: Moira L
authors.initials: ML
authors.lastname: Steyn-Ross
authors.forename: D A
authors.initials: DA
authors.lastname: Steyn-Ross
authors.forename: J W
authors.initials: JW
authors.lastname: Sleigh
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000758:Anesthesia; D018681:Anesthetics, General / Q000494:pharmacology*; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D003198:Computer Simulation; D004569:Electroencephalography / Q000187:drug effects* / Q000379:methods; D006801:Humans; D008959:Models, Neurological; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014474:Unconsciousness / Q000139:chemically induced / Q000503:physiopathology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D018681:Anesthetics, General; D005680:gamma-Aminobutyric Acid