• R E Kallionpää, A Scheinin, R A Kallionpää, N Sandman, M Kallioinen, R Laitio, T Laitio, K Kaskinoro, T Kuusela, A Revonsuo, H Scheinin, and K Valli.
• Department of Psychology and Speech-Language Pathology, and Turku Brain and Mind Center, University of Turku, Turku, Finland; Department of Perioperative Services, Intensive Care and Pain Medicine, Turku University Hospital, Turku, Finland. Electronic address: roosa.kallionpaa@utu.fi.
• Br J Anaesth. 2018 Jul 1; 121 (1): 270-280.

BackgroundStudying the effects of anaesthetic drugs on the processing of semantic stimuli could yield insights into how brain functions change in the transition from wakefulness to unresponsiveness. Here, we explored the N400 event-related potential during dexmedetomidine- and propofol-induced unresponsiveness.MethodsForty-seven healthy subjects were randomised to receive either dexmedetomidine (n=23) or propofol (n=24) in this open-label parallel-group study. Loss of responsiveness was achieved by stepwise increments of pseudo-steady-state plasma concentrations, and presumed loss of consciousness was induced using 1.5 times the concentration required for loss of responsiveness. Pre-recorded spoken sentences ending either with an expected (congruous) or an unexpected (incongruous) word were presented during unresponsiveness. The resulting electroencephalogram data were analysed for the presence of the N400 component, and for the N400 effect defined as the difference between the N400 components elicited by congruous and incongruous stimuli, in the time window 300-600 ms post-stimulus. Recognition of the presented stimuli was tested after recovery of responsiveness.ResultsThe N400 effect was not observed during dexmedetomidine- or propofol-induced unresponsiveness. The N400 component, however, persisted during dexmedetomidine administration. The N400 component elicited by congruous stimuli during unresponsiveness in the dexmedetomidine group resembled the large component evoked by incongruous stimuli at the awake baseline. After recovery, no recognition of the stimuli heard during unresponsiveness occurred.ConclusionsDexmedetomidine and propofol disrupt the discrimination of congruous and incongruous spoken sentences, and recognition memory at loss of responsiveness. However, the processing of words is partially preserved during dexmedetomidine-induced unresponsiveness.Clinical Trial RegistrationNCT01889004.Copyright © 2018 The Author(s). Published by Elsevier Ltd.. All rights reserved.

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