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.
LSD increases global brain synchrony and dynamic complexity by stabilizing a globally synchronized, functionally non-modular brain state that acts as an attractor, recruiting transitions from cognitive control networks. This enhanced synchrony arises from a convergence of excitatory/inhibitory balance across cortical hierarchies, driven by suppression in sensorimotor cortices and potentiation in transmodal regions. Sensorimotor cortices emerge as potential regulatory hubs for this rebalancing. The resulting brain state shows weakened sensory anchoring and enhanced cognitive flexibility, blurring the line between concrete perception and abstract cognition. This neurophysiological remodeling may underlie LSD's hallucinatory effects and its therapeutic potential for mental disorders with rigid thought patterns.