Connectivity biomarkers can differentiate patients with different levels of consciousness

• No voluntary brain activation is needed to examine the level of consciousness.
• Connectivity in the EEG distinguishes different levels of consciousness.
• Partialized coherence, directed transfer function, and generalized partial directed coherence distinguish MCS from VS patients.

ObjectiveIn the present study, we searched for resting-EEG biomarkers that distinguish different levels of consciousness on a single subject level with an accuracy that is significantly above chance.MethodsWe assessed 44 biomarkers extracted from the resting EEG with respect to their discriminative value between groups of minimally conscious (MCS, N = 22) patients, vegetative state patients (VS, N = 27), and – for a proof of concept – healthy participants (N = 23). We applied classification with support vector machines.ResultsPartial coherence, directed transfer function, and generalized partial directed coherence yielded accuracies that were significantly above chance for the group distinction of MCS vs. VS (.88, .80, and .78, respectively), as well as healthy participants vs. MCS (.96, .87, and .93, respectively) and VS (.98, .84, and .96, respectively) patients.ConclusionsThe concept of connectivity is crucial for determining the level of consciousness, supporting the view that assessing brain networks in the resting state is the golden way to examine brain functions such as consciousness.SignificanceThe present results directly show that it is possible to distinguish patients with different levels of consciousness on the basis of resting-state EEG.