title: Probing ERP correlates of verbal semantic processing in patients with impaired consciousness.
abstract: Our ability to identify covert cognitive abilities in non-communicating patients is of prime importance to improve diagnosis, to guide therapeutic decisions and to better predict their cognitive outcome. In the present study, we used a basic and rigorous paradigm contrasting pairs of words orthogonally. This paradigm enables the probing of semantic processing by comparing neural activity elicited by similar words delivered in various combinations. We describe the respective timing, topography and estimated cortical sources of two successive event-related potentials (ERP) components (N400 and late positive component (LPC)) using high-density EEG in conscious controls (N=20) and in minimally conscious (MCS; N=15) and vegetative states (VS; N=15) patients recorded at bedside. Whereas N400-like ERP components could be observed in the VS, MCS and conscious groups, only MCS and conscious groups showed a LPC response, suggesting that this late effect could be a potential specific marker of conscious semantic processing. This result is coherent with recent findings disentangling early and local non-conscious responses (e.g.: MMN in odd-ball paradigms, N400 in semantic violation paradigms) from late, distributed and conscious responses (e.g.: P3b to auditory rule violation) in controls and in patients with disorders of consciousness. However, N400 and LPC responses were not easily observed at the individual level, - even in conscious controls - , with standard ERP analyses, which is a limiting factor for its clinical use. Of potential interest, the only 3 patients presenting both significant N400 and LPC effects were MCS, and 2 of them regained consciousness and functional language abilities.
authors.affiliation: AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Intensive Care Unit, Department of Neurology, Paris, France; INSERM, U 1127, F-75013 Paris, France; Institut du Cerveau et de la Moelle épinière, ICM, PICNIC Lab, F-75013 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Rohaut
authors.affiliation: AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Department of Neurophysiology, Paris, France; INSERM, U 1127, F-75013 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Faugeras
authors.affiliation: AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Department of Neurophysiology, Paris, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Chausson
authors.affiliation: INSERM, U 1127, F-75013 Paris, France; Institut du Cerveau et de la Moelle épinière, ICM, PICNIC Lab, F-75013 Paris, France.
authors.forename: Jean-Rémi
authors.initials: JR
authors.lastname: King
authors.affiliation: INSERM, U 1127, F-75013 Paris, France; Institut du Cerveau et de la Moelle épinière, ICM, PICNIC Lab, F-75013 Paris, France.
authors.forename: Imen El
authors.initials: IE
authors.lastname: Karoui
authors.affiliation: AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Department of Neurology, Paris, France; INSERM, U 1127, F-75013 Paris, France; Institut du Cerveau et de la Moelle épinière, ICM, PICNIC Lab, F-75013 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Cohen
authors.affiliation: AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Department of Neurology, Paris, France; AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Department of Neurophysiology, Paris, France; INSERM, U 1127, F-75013 Paris, France; Institut du Cerveau et de la Moelle épinière, ICM, PICNIC Lab, F-75013 Paris, France; Sorbonne Universités, UPMC Univ Paris 06, Faculté de Médecine Pitié-Salpêtrière, Paris, France. Electronic address: lionel.naccache@psl.aphp.fr.
authors.forename: Lionel
authors.initials: L
authors.lastname: Naccache
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000368:Aged; D002540:Cerebral Cortex / Q000503:physiopathology*; D003244:Consciousness Disorders / Q000175:diagnosis / Q000503:physiopathology*; D004569:Electroencephalography; D005071:Evoked Potentials; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012660:Semantics; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult
keywords: Consciousness; Evoked potentials; LPC (P600); Language; Minimally conscious state; N400; Prognosis; Vegetative state