In humans, the psychedelic state induced by ketamine is associated with increased diversity and complexity of spontaneous electroencephalography (EEG) signals, but not of evoked EEG responses. This suggests that ketamine's effects on brain dynamics are specific to ongoing, internally generated neural activity rather than to stimulus-driven responses. The finding points to a potential neural marker of altered consciousness under psychedelics.
Measures that distinguish conscious from unconscious brain states may also be influenced by attentional load and cognitive resource use within conscious states. Testing several proposed measures, the study examines whether they are modulated by changes in attention and cognitive demands, which has rarely been tested before. The findings suggest that these measures are not solely markers of consciousness but can vary with attentional load within conscious states.