Review: Quantifying conscious level by means of intrinsic brain connectivity

Consciousness is seemingly lost and recovered every day, from the moment we fall asleep until we wake up. Although these departures from wakefulness bring about different changes in brain function, behavior, and neurochemistry, they all lead to lack of reported subjective experience. Here, I will show how the temporal dynamics of ongoing brain activity have characterized different states of unconsciousness, such as sleep, pharmacologically-induced anesthesia in humans and animals, and in noncommunicating states following to brain injury. By and large, these investigations indicate that during unconscious states cortical long-range correlations are disrupted in both space and time, anticorrelated cortical interactions disappear, and the dynamic explorations are limited to specific patterns which are dominated by rigid functional configurations tied to the anatomical connectivity.