RT Journal Article SR Electronic T1 A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior JF Science Translational Medicine FD American Association for the Advancement of Science SP 198ra105 OP 198ra105 DO 10.1126/scitranslmed.3006294 VO 5 IS 198 A1 Casali, Adenauer G. A1 Gosseries, Olivia A1 Rosanova, Mario A1 Boly, Mélanie A1 Sarasso, Simone A1 Casali, Karina R. A1 Casarotto, Silvia A1 Bruno, Marie-Aurélie A1 Laureys, Steven A1 Tononi, Giulio A1 Massimini, Marcello YR 2013 UL http://stm.sciencemag.org/content/5/198/198ra105.abstract AB One challenging aspect of the clinical assessment of brain-injured, unresponsive patients is the lack of an objective measure of consciousness that is independent of the subject’s ability to interact with the external environment. Theoretical considerations suggest that consciousness depends on the brain’s ability to support complex activity patterns that are, at once, distributed among interacting cortical areas (integrated) and differentiated in space and time (information-rich). We introduce and test a theory-driven index of the level of consciousness called the perturbational complexity index (PCI). PCI is calculated by (i) perturbing the cortex with transcranial magnetic stimulation (TMS) to engage distributed interactions in the brain (integration) and (ii) compressing the spatiotemporal pattern of these electrocortical responses to measure their algorithmic complexity (information). We test PCI on a large data set of TMS-evoked potentials recorded in healthy subjects during wakefulness, dreaming, nonrapid eye movement sleep, and different levels of sedation induced by anesthetic agents (midazolam, xenon, and propofol), as well as in patients who had emerged from coma (vegetative state, minimally conscious state, and locked-in syndrome). PCI reliably discriminated the level of consciousness in single individuals during wakefulness, sleep, and anesthesia, as well as in patients who had emerged from coma and recovered a minimal level of consciousness. PCI can potentially be used for objective determination of the level of consciousness at the bedside.