Electroencephalogram signatures of ketamine anesthesia-induced unconsciousness

• Slow-delta oscillations that alternate with gamma oscillations (gamma burst) occur with ketamine at general anesthesia levels.
• Gamma, theta and decreased alpha/beta oscillations are not unique to ketamine at general anesthesia levels.
• The gamma burst pattern may result from circuit disruptions in cortical and subcortical sites.

ObjectivesKetamine 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.MethodsWe 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.ResultsFollowing 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 (∼27–40 Hz) oscillations. This pattern was also associated with increased theta oscillations (∼4–8 Hz) and decreased alpha/beta oscillations (∼10–24 Hz).ConclusionsKetamine anesthesia-induced unconsciousness is associated with a gamma burst EEG pattern.SignificanceThe EEG signature of ketamine anesthesia-induced unconsciousness may offer new insights into NMDA circuit mechanisms for unconsciousness.