The vividness of conscious experience is linked to brain dynamics. Propofol and ketamine, both anesthetics, produce different subjective states. This study examined how these drugs alter the structure of dynamic attractors reconstructed from electrical brain activity recorded from the cerebral cortex of two macaques. The awake condition showed the richest structure, visiting the most states with pronounced higher-order dynamics and the least deterministic activity. Propofol produced the most dissimilar dynamics, shifting to an impoverished, constrained, low-structure regime. Ketamine combined aspects of both: generally less complex than awake but well above propofol on almost all measures. These results offer deeper insights than typical point-measures of complexity.
The brain may operate near a critical tipping point, a state thought necessary for consciousness and complex cognition. Using invasive ECoG recordings from a macaque transitioning between consciousness and unconsciousness under propofol and ketamine, the study found that propofol dramatically restricted the size and duration of neural avalanches and reduced the complexity of brain dynamics, while ketamine allowed more awake-like dynamics to persist. Despite these differences, all states showed some signs of persistent criticality when tested for exponent relations and universal shape-collapse, suggesting that maintenance of critical brain dynamics may be important for regulating conscious awareness.