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Curr Biol. 2015 Dec 7;25(23):3099-105. doi: 10.1016/j.cub.2015.10.014. Epub 2015 Nov 19.

Consciousness and Complexity during Unresponsiveness Induced by Propofol, Xenon, and Ketamine.

Author information

1
Dipartimento di Scienze Biomediche e Cliniche "L. Sacco", Università degli Studi di Milano, 20157 Milan, Italy.
2
Department of Psychiatry, University of Wisconsin-Madison, Madison, WI 53719, USA; Department of Neurology, University of Wisconsin-Madison, Madison, WI 53705, USA.
3
Dipartimento di Scienze Biomediche e Cliniche "L. Sacco", Università degli Studi di Milano, 20157 Milan, Italy; Dipartimento di Scienze Clinico-chirurgiche, Diagnostiche e Pediatriche, Sezione di Anestesia Rianimazione e Terapia Antalgica, Università degli Studi di Pavia, SC Anestesia e Rianimazione, Fondazione IRCCS Policlinico S. Matteo, 27100 Pavia, Italy.
4
Department of Psychiatry, University of Wisconsin-Madison, Madison, WI 53719, USA; Coma Science Group, University and University Hospital of Liège, GIGA-Research B34, 4000 Liège, Belgium.
5
Coma Science Group, University and University Hospital of Liège, GIGA-Research B34, 4000 Liège, Belgium.
6
Institute of Science and Technology, Federal University of São Paulo, 12231-280 São José dos Campos, Brazil.
7
Department of Anesthesia and Intensive Care Medicine, CHU Sart Tilman University Hospital, University of Liège, 4000 Liège, Belgium.
8
Department of Anaesthesiology, University Hospitals of the KU Leuven, KU Leuven, 3000 Leuven, Belgium; Department of Cardiovascular Sciences, University Hospitals of the KU Leuven, KU Leuven, 3000 Leuven, Belgium.
9
Department of Psychiatry, University of Wisconsin-Madison, Madison, WI 53719, USA.
10
Coma Science Group, University and University Hospital of Liège, GIGA-Research B34, 4000 Liège, Belgium. Electronic address: steven.laureys@ulg.ac.be.
11
Dipartimento di Scienze Biomediche e Cliniche "L. Sacco", Università degli Studi di Milano, 20157 Milan, Italy; Istituto Di Ricovero e Cura a Carattere Scientifico, Fondazione Don Carlo Gnocchi, 20148 Milan, Italy. Electronic address: marcello.massimini@unimi.it.

Abstract

A common endpoint of general anesthetics is behavioral unresponsiveness, which is commonly associated with loss of consciousness. However, subjects can become disconnected from the environment while still having conscious experiences, as demonstrated by sleep states associated with dreaming. Among anesthetics, ketamine is remarkable in that it induces profound unresponsiveness, but subjects often report "ketamine dreams" upon emergence from anesthesia. Here, we aimed at assessing consciousness during anesthesia with propofol, xenon, and ketamine, independent of behavioral responsiveness. To do so, in 18 healthy volunteers, we measured the complexity of the cortical response to transcranial magnetic stimulation (TMS)--an approach that has proven helpful in assessing objectively the level of consciousness irrespective of sensory processing and motor responses. In addition, upon emergence from anesthesia, we collected reports about conscious experiences during unresponsiveness. Both frontal and parietal TMS elicited a low-amplitude electroencephalographic (EEG) slow wave corresponding to a local pattern of cortical activation with low complexity during propofol anesthesia, a high-amplitude EEG slow wave corresponding to a global, stereotypical pattern of cortical activation with low complexity during xenon anesthesia, and a wakefulness-like, complex spatiotemporal activation pattern during ketamine anesthesia. Crucially, participants reported no conscious experience after emergence from propofol and xenon anesthesia, whereas after ketamine they reported long, vivid dreams unrelated to the external environment. These results are relevant because they suggest that brain complexity may be sensitive to the presence of disconnected consciousness in subjects who are considered unconscious based on behavioral responses.

PMID:
26752078
DOI:
10.1016/j.cub.2015.10.014
[Indexed for MEDLINE]
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