Slow cortico-cortical connectivity (2-5Hz) is a new robust signature of conscious states

While long-range cortico-cortical functional connectivity has been reported by several studies as a necessary condition of conscious state, precise empirical evidence is still scarce. In the present work we provide such a direct and conclusive evidence in a set of three experiments. In the two first experiments intracranial-EEG was recorded during four distinct states in the same individuals: conscious wakefulness (CW), rapid-eye-movement sleep (REM), stable periods of slow-wave sleep (SWS) and deep propofol anaesthesia (PA). We discovered that long-range FC, computed by the weighted Symbolic-Mutual-Information (wSMI) in the 2-5Hz frequency band was a specific marker of conscious states that could discriminate CW and REM from SWS and PA. In the third experiment, we generalized this original finding on a large cohort of brain-injured patients by revealing that wSMI in the 2-5 Hz range was also able to accurately discriminate patients in the vegetative state (or unresponsive wakefulness syndrome) from patients in the minimally conscious state. Taken together the present results suggest that 2-5Hz FC is a new and robust signature of conscious states.