"Recently we have proposed that consciousness depends critically not so much on firing rates, synchronization at specific frequency
bands, or sensory input per se, but rather on the brain_s ability to integrate information, which is contingent on the effective connectivity among
functionally specialized regions of the thalamocortical system. Effective connectivity refers to the ability of a set of neuronal groups to causally affect the firing of other neuronal groups within a system. The fading of consciousness during NREM sleep episodes early in the night, evidenced by short or blank reports of cognitive activity upon awakening , would then be associated with an impairment of cortical effective connectivity."
A review paper:
Neural correlates of consciousness: progress and problems \cite{koch2016neural}
Section 'Neurophysiology -activated EEG', for a crash course in classifying EEG into wake/sleep and why this is a good but not perfect indication of consciousness.
Section 'Neural differentiation and integration', for a crash course in the role of differentation and integration in consciousness, and the PCI metric.