A brain-based measure called the Perturbational Complexity Index (PCI) can reliably distinguish conscious from unconscious individuals, even when they cannot speak or move. The index was first validated in 150 healthy and brain-injured people who could report their conscious state, achieving perfect accuracy in separating conscious from unconscious conditions. Applied to 81 noncommunicative patients, PCI correctly identified 94.7% of those in a minimally conscious state and revealed that 9 of 43 patients diagnosed as vegetative had PCI values overlapping with conscious individuals. These findings suggest that some behaviorally unresponsive patients may retain hidden conscious capacity.
Functional connectivity within two brain networks plays distinct roles in disorders of consciousness. Connectivity in the salience network, particularly between the supragenual anterior cingulate cortex and left anterior insula, was reduced in patients with unresponsive wakefulness syndrome compared to those in a minimally conscious state or fully conscious brain-lesioned patients. This connectivity correlated with behavioral signs of consciousness. In contrast, connectivity in the default-mode network, specifically between the posterior cingulate cortex and left lateral parietal cortex, was weaker in patients with unresponsive wakefulness syndrome who did not recover compared to those who later emerged from this state, suggesting this network predicts recovery of consciousness.