Journal
SCIENCE TRANSLATIONAL MEDICINE
Volume 5, Issue 198, Pages -Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/scitranslmed.3006294
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Funding
- Belgian National Funds for Scientific Research (FNRS)
- EU [FP7-ICT-2011-9, 600806]
- PUR
- Dote ricerca: FSE, Regione Lombardia (University of Milan)
- Prin2008 (Italian Government)
- Fonds Leon Fredericq, James S. McDonnell Foundation
- Mind Science Foundation
- European Commission (Mindbridge, DISCOS, DECODER COST)
- Concerted Research Action [ARC 06/11-340]
- Public Utility Foundation Universite Europeenne du Travail
- Fondazione Europea di Ricerca Biomedica
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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.
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