Ketamine, an anesthetic that blocks NMDA receptors, produces alternating bursts of gamma (25-50 Hz) and slow-delta (0.1-4 Hz) brain oscillations. A hidden Markov model fitted to local field potentials from two non-human primates and electroencephalograms from nine humans quantified these dynamics. Gamma activity lasted on average 2.2 seconds in one primate, 1.2 in the other, and 2.5 in humans; slow-delta lasted 1.6, 1.0, and 1.8 seconds respectively. Five sub-states with regular sequential transitions were identified. These findings provide quantitative constraints for models of rhythm generation underlying ketamine-induced altered arousal.
Ketamine, an anesthetic and psychoactive drug, produces alternating patterns of brain activity: bursts of gamma oscillations (30-50 Hz) and slow oscillations (0.1-10 Hz). A hidden Markov model (HMM) was applied to brainwave data from two non-human primates and nine human subjects receiving anesthetic doses of ketamine. The model revealed distinct states corresponding to gamma bursts and slow oscillations, with intermediate states. Mean gamma burst durations were 2.5 seconds (non-human primate 1), 1.2 seconds (non-human primate 2), and 2.7 seconds (humans). Mean slow oscillation durations were 1.6 seconds, 0.7 seconds, and 2.8 seconds, respectively. This framework provides quantitative constraints for understanding how ketamine alters states of consciousness.