Down but not out: drugs that enhance delta oscillations but preserve consciousness

Delta (1 – 4 Hz) EEG/MEG activity is generally indicative of loss of consciousness and cortical down states, particularly when it is diffuse and high amplitude. Remarkably, however, drug challenge studies of several diverse classes of pharmacological agents—including antiepileptics, GABA-B-ergics, anticholinergics, and psychedelic tryptamines—demonstrate that participants appear to be neurophysiologically “down” (EEG activity resembling cortical down states) even when they are not psychologically “out” (unconscious). Of those substances that are safe to use in healthy volunteers, some may be highly valuable research tools for investigating which neural activity patterns are sufficient for consciousness or its absence.