In rats under propofol, sevoflurane, and ketamine anesthesia, the perturbational complexity index (PCI) and two spontaneous EEG measures—Lempel-Ziv complexity (LZ) and geometric integrated information (ΦG)—best distinguished awake from anesthetized states for propofol and sevoflurane. However, PCI was anti-correlated with spontaneous measures of integrated information, which increased during propofol and sevoflurane anesthesia, contrary to expectations. The divergence suggests anesthesia disrupts global cortico-cortical information transfer, while spontaneous activity suggests the opposite, possibly due to suppressed encoding specificity or driving subcortical projections. Perturbation-based and spontaneous measures may be complementary for studying altered consciousness.
The cerebral cortex generates diverse patterns of activity that shift across brain states such as sleep, wakefulness, anesthesia, and disorders of consciousness, yet a unified definition of brain states remains elusive. This review focuses on two extremes: synchronous states, which predominantly underlie unconsciousness, and asynchronous states, which predominantly underlie consciousness, though exceptions exist. The authors integrate data across levels from local circuits to whole-brain dynamics, examining properties like cortical complexity, functional connectivity, synchronization, wave propagation, and excitatory-inhibitory balance. They make experimental and clinical data, as well as computational models at micro-, meso-, and macrocortical levels, available to readers.