Insights of neurophysiology on unconscious state using combined transcranial magnetic stimulation and electroencephalography: A systematic review

Naohiro Arai, Tomoya Nakanishi, Shinichiro Nakajima, Xuemei Li, Masataka Wada, Zafiris J. Daskalakis, Michelle S. Goodman, Daniel M. Blumberger, Masaru Mimura, Yoshihiro Noda

Research output: Contribution to journalReview articlepeer-review

Abstract

Unconscious state has been investigated in numerous studies so far, but pathophysiology of this state is not fully understood. Recently, combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) has been developed to allow for non-invasive assessment of neurophysiology in the cerebral cortex. We conducted a systematic literature search for TMS-EEG studies on human unconscious state using PubMed with cross-reference and manual searches. The initial search yielded 137 articles, and 19 of them were identified as relevant, including one article found by manual search. This review included 10 studies for unresponsive wakefulness syndrome (UWS), 9 for minimally conscious states (MCS), 5 for medication-induced unconscious states, and 6 for natural non-rapid eye movement states. These studies analyzed TMS-evoked potential to calculate perturbational complexity index (PCI) and OFF-periods. In particular, PCI was found to be a potentially useful marker to differentiate between UWS and MCS. This review demonstrated that TMS-EEG could represent a promising neuroscientific tool to investigate various unconscious states. Further TMS-EEG research may help elucidate the neural basis of unconscious state.

Original languageEnglish
Pages (from-to)293-312
Number of pages20
JournalNeuroscience and Biobehavioral Reviews
Volume131
DOIs
Publication statusPublished - 2021 Dec

Keywords

  • Disorders of consciousness
  • Minimally conscious state
  • Perturbational complexity index
  • TMS-EEG
  • Unconscious state
  • Unresponsive wakefulness syndrome

ASJC Scopus subject areas

  • Neuropsychology and Physiological Psychology
  • Cognitive Neuroscience
  • Behavioral Neuroscience

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