Low-frequency delta-band neural activity is typically associated with loss of consciousness and cortical down states, especially when diffuse and high amplitude. However, several classes of pharmacological agents—including antiepileptic drugs, GABA B receptor activators, acetylcholine receptor blockers, and psychedelics—can produce neural activity resembling cortical down states while participants remain conscious. Among these substances safe for healthy volunteers, some may serve as valuable research tools for determining which neural activity patterns are sufficient for consciousness or its absence.
Consciousness likely cannot begin before the establishment of thalamocortical connectivity at 26 weeks gestation, as this system is necessary for subjective experience according to most theoretical frameworks. To determine when consciousness emerges after this point, the authors advocate developing a sensory perturbational complexity index (sPCI) using auditory, visual, or olfactory cortical perturbations—rather than electromagnetic ones—to estimate the perinatal brain's state of consciousness. Techniques such as fMRI, EEG, and MEG can be used in both newborn and fetal studies, with the womb offering a more controlled environment than the cradle for such investigations.