King et al. make measurements they suggest are a signature of conscious state in awake but noncommunicating patients. I pass on the summary, abstract, and one of their figures (and, the first graphic, thanks to Jean-Rémi King, who offers the unedited PDF of the article here):
Highlights
• Theories of consciousness link conscious access to global information integration
• 181 EEG recordings were acquired, including 143 from VS and MCS patients
• Information sharing across current sources was estimated with a new measure
• The results suggest that unconscious patients have lower global information sharing
Summary
Neuronal theories of conscious access tentatively relate conscious perception to the integration and global broadcasting of information across distant cortical and thalamic areas. Experiments contrasting visible and invisible stimuli support this view and suggest that global neuronal communication may be detectable using scalp electroencephalography (EEG). However, whether global information sharing across brain areas also provides a specific signature of conscious state in awake but noncommunicating patients remains an active topic of research. We designed a novel measure termed “weighted symbolic mutual information” (wSMI) and applied it to 181 high-density EEG recordings of awake patients recovering from coma and diagnosed in various states of consciousness. The results demonstrate that this measure of information sharing systematically increases with consciousness state, particularly across distant sites. This effect sharply distinguishes patients in vegetative state (VS), minimally conscious state (MCS), and conscious state (CS) and is observed regardless of etiology and delay since insult. The present findings support distributed theories of conscious processing and open up the possibility of an automatic detection of conscious states, which may be particularly important for the diagnosis of awake but noncommunicating patients.
Figure - wSMI Increases with Consciousness, Primarily over Centroposterior Regions(A) The median wSMI that each EEG channel shares with all other channels is depicted for each state of consciousness.(B) 120 pairs formed by 16 clusters of EEG channels are depicted as 3D arcs whose height is proportional to the Euclidian distance separating the two clusters. Line color and thickness are proportional to the mean wSMI shared by the corresponding cluster pair.
