Stratification of unresponsive patients by an independently validated index of brain complexity.
Level 3 - non-randomized controlled study
Diagnostic derivation and validation study across benchmark and clinical cohort groups
PubMed 27717082 · doi:10.1002/ana.24779
What was done
Researchers evaluated the diagnostic accuracy of the Perturbational Complexity Index (PCI) for assessing consciousness. The metric was first benchmarked in 150 healthy controls and communicative brain-injured individuals across conscious wakefulness, disconnected consciousness, and unconsciousness who could confirm their state via subjective report. Using receiver operating characteristic curve analysis, an optimal cutoff was derived and subsequently applied to 81 noncommunicative patients with disorders of consciousness (38 in a minimally conscious state [MCS] and 43 in a vegetative state [VS]).
What was found
In the benchmark population, the empirical cutoff separated conscious and unconscious conditions with 100% sensitivity and 100% specificity. When applied to noncommunicative patients, the cutoff demonstrated 94.7% sensitivity in detecting MCS (36 of 38) and classified 9 of 43 vegetative state patients (20.9%) as having high PCI values overlapping with conscious benchmark distributions.
Why it matters
PCI provides a validated, behavior-independent electrophysiological metric to stratify unresponsive patients. It demonstrates that a subset of patients clinically categorized as vegetative may retain brain complexity levels consistent with capacity for consciousness.
Limits
Behaviorally unresponsive vegetative state patients cannot provide subjective report, precluding direct verification of ground truth consciousness in that subgroup. The abstract does not detail patient etiologies, time post-injury, or longitudinal clinical outcomes.
Cited by
- supports Brain complexity measured by TMS-EEG and Lempel-Ziv complexity is high during wakefulness, dream states, and ketamine-induced dissociation, but low during non-REM deep sleep, anesthesia, and brain death.
- supports The Perturbational Complexity Index (PCI) has an empirical cutoff threshold at 0.31 to differentiate conscious from unconscious individuals.