Traveling cortical waves in the 3-6 Hz range coordinate neuronal activity across visual and parietal cortex only in brain states where perception is possible. In awake mice, visual stimuli reset spontaneous waves, producing stimulus-evoked feedback waves that entrain neurons. Under anesthesia, visual stimuli fail to disrupt spontaneous waves. During ketamine-induced dissociation, spontaneous waves themselves traverse the cortex caudally and entrain neurons, mimicking the stimulus-evoked pattern seen in wakefulness. Thus, coordinated neuronal assemblies orchestrated by traveling waves emerge in states that allow perception, but only the awake state reliably links this coordination to external visual input.
During wakefulness, people respond to external stimuli, while in dreams or drug-induced dissociated states, vivid internal experiences occur with reduced perception of the outside world. The brain's activity near a critical point between damped and exploding oscillations is linked to conscious experience, and this signature appears in both normal wakefulness and dissociative states but not in dreamless sleep or anesthesia. Using high-density EEG in human male volunteers given escalating ketamine doses, activity became progressively more stable, especially at higher frequencies, as dissociative symptoms increased. This stabilization correlated with reduced ability to perceive external stimuli, not with conscious experience itself. Combining statistical and dynamical measures of criticality may help distinguish wakefulness, dissociation, and unconsciousness.