“…Many features of brain electrophysiology have been investigated and reported to correlate with different conscious processes or even the level of consciousness. Spectral power differences have been commonly found at characteristic frequency bands; notably, lack of consciousness has been associated with increased power at low frequencies (delta waves: <4 Hz) in multiple contexts, including sleep stage depth, dream recall within a sleep stage, and anaesthetic depth (Chellappa et al, 2011;Evans, 2003;Hobson & Pace-Schott, 2002;Murphy et al, 2011;Scarpelli et al, 2017;Siclari et al, 2017Siclari et al, , 2018Thomsen, Rosenfalck, & Nørregaard Christensen, 1991). Higher levels of consciousness (or arousal) have also been suggested to correlate with a lower spectral exponent (Colombo et al, 2019), higher signal entropy or complexity (Bein, 2006;Bruhn, Röpcke, & Hoeft, 2000;D'Andola et al, 2017;Hudetz, Liu, Pillay, Boly, & Tononi, 2016;King et al, 2013;Liang et al, 2013;Ouyang, Li, Liu, & Li, 2013;Sarasso et al, 2015;Schartner et al, 2015), stronger phase coherence between brain areas (Bola et al, 2017;Lee et al, 2017;Mikulan et al, 2017), and more causally integrated brain areas (Barrett et al, 2012;D'Andola et al, 2017;Fasoula, Attal, & Schwartz, 2013).…”