Detecting the potential for consciousness in unresponsive patients using the perturbational complexity index

Dmitry O. Sinitsyn, Alexandra G. Poydasheva, Ilya S. Bakulin, Liudmila A. Legostaeva, Elizaveta G. Iazeva, Dmitry V. Sergeev, Anastasia N. Sergeeva, Elena I. Kremneva, Sofya N. Morozova, Dmitry Yu Lagoda, Silvia Casarotto, Angela Comanducci, Yulia V. Ryabinkina, Natalia A. Suponeva, Michael A. Piradov

Research output: Contribution to journalArticlepeer-review


The difficulties of behavioral evaluation of prolonged disorders of consciousness (DOC) motivate the development of brain-based diagnostic approaches. The perturbational complexity index (PCI), which measures the complexity of electroencephalographic (EEG) responses to transcranial magnetic stimulation (TMS), showed a remarkable sensitivity in detecting minimal signs of consciousness in previous studies. Here, we tested the reliability of PCI in an independently collected sample of 24 severely brain-injured patients, including 11 unresponsive wakefulness syndrome (UWS), 12 minimally conscious state (MCS) patients, and 1 emergence from MCS patient. We found that the individual maximum PCI value across stimulation sites fell within the consciousness range (i.e., was higher than PCI*, which is an empirical cutoff previously validated on a benchmark population) in 11 MCS patients, yielding a sensitivity of 92% that surpassed qualitative evaluation of resting EEG. Most UWS patients (n = 7, 64%) showed a slow and stereotypical TMS-EEG response, associated with low-complexity PCI values (i.e., ≤PCI*). Four UWS patients (36%) provided high-complexity PCI values, which might suggest a covert capacity for consciousness. In conclusion, this study successfully replicated the performance of PCI in discriminating between UWS and MCS patients, further motivating the application of TMS-EEG in the workflow of DOC evaluation.

Original languageEnglish
Article number917
Pages (from-to)1-12
Number of pages12
JournalBrain Sciences
Issue number12
Publication statusPublished - Dec 2020


  • Diagnosis
  • Disorders of consciousness
  • Electroencephalography
  • Minimally conscious state
  • Perturbational complexity index
  • Reliability
  • Transcranial magnetic stimulation
  • Unresponsive wakefulness syndrome

ASJC Scopus subject areas

  • Neuroscience(all)


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