Directional connectivity in the EEG is able to discriminate wakefulness from NREM sleep.
Physiological measurement August 22, 2017 G Lioi, S L Bell, D C Smith et al.
Directed coherence, a measure of directional connectivity between brain regions, was assessed as an index of consciousness level during non-REM sleep. Polysomnographic recordings from ten healthy subjects showed that while all EEG measures could distinguish NREM sleep from waking at the group level, individual variation was considerable. Across individuals, normalized power, strength of long-range connections, and direction of functional links strongly correlated with NREM sleep stages. At the individual level, the direction of functional links was the most reliable index, highly correlating with each subject's sleep timeline. Directed coherence offers a promising method for assessing consciousness, grounded in current understanding of disrupted connectivity and impaired information flow.