Electroencephalogram signatures of ketamine anesthesia-induced unconsciousness

Objectives: Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist commonly administered as a general anesthetic. However, neural circuit mechanisms to explain ketamine anesthesia-induced unconsciousness in humans are yet to be clearly defined. Disruption of frontal-parietal network connectivity has been proposed as a mechanism to explain this brain state. However, this mechanism was recently demonstrated at subanesthetic doses of ketamine in awake-patients. Therefore, we investigated whether there is an electroencephalogram (EEG) signature specific for ketamine anesthesia-induced unconsciousness. Methods: We retrospectively studied the EEG in 12 patients who received ketamine for the induction of general anesthesia. We analyzed the EEG dynamics using power spectral and coherence methods. Results: Following the administration of a bolus dose of ketamine to induce unconsciousness, we observed a "gamma burst" EEG pattern that consisted of alternating slow-delta (0.1-4 Hz) and gamma (similar to 27-40 Hz) oscillations. This pattern was also associated with increased theta oscillations (similar to 4-8 Hz) and decreased alpha/beta oscillations (similar to 10-24 Hz). Conclusions: Ketamine anesthesia-induced unconsciousness is associated with a gamma burst EEG pattern. Significance: The EEG signature of ketamine anesthesia-induced unconsciousness may offer new insights into NMDA circuit mechanisms for unconsciousness. (C) 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.