A framework is introduced that characterizes neuronal markers of consciousness along two dimensions: how well they distinguish conscious from non-conscious states (x-axis) and how well they distinguish different conscious contents (y-axis). Using electroencephalography markers of connectivity, complexity, and spectral summaries, the framework is applied to healthy participants during a nap and patients with disorders of consciousness for the state dimension, and to healthy participants in visual awareness and auditory local-global paradigms for the content dimension. Separate clusters of markers with correlated and anticorrelated dynamics emerge, highlighting the complex relationship between the state and content of consciousness and the need to consider them together.
Patients with disorders of consciousness (DoC), such as vegetative state (VS) or minimally conscious state (MCS), offer a unique way to test theories about consciousness by dissociating vigilance from conscious experience. This article reviews major findings in DoC research, proposes a taxonomy, and highlights limitations. A purely behavioral approach is insufficient to assess conscious state. Comparing MCS and VS does not provide a clean contrast between conscious and unconscious states. Based on resting-state PET data, behavioral MCS reflects a cortically mediated state that does not necessarily imply preserved consciousness.