40 Hz auditory steady-state responses in patients with disorders of consciousness: Correlation between phase-locking index and Coma Recovery Scale-Revised score

Objective: We aimed to elucidate whether 40 Hz auditory steady-state response (ASSR) could be sensitive to the state of patients with disorders of consciousness (DOC) as estimated with Coma Recovery Scale-Revised (CRS-R) diagnostic tool. Methods: Fifteen DOC patients and 24 healthy controls took part in the study. The 40 Hz click trains were used to evoke ASSRs. Mean evoked amplitude (EA) and phase-locking index (PLI) within 38-42 Hz window were calculated for 100 ms bins, starting from -200 to 700 ms relative to stimulus onset. Results: The PLI values from the patient group in the period of 200-500 ms after the stimulus onset positively correlated with the CRS-R total score and with the scores of the Auditory and Visual subscales. Conclusions: The phase-locking index of 40 Hz auditory steady-state responses can be an indicator of the level of dysfunction of the central nervous system in DOC. Significance: Our results emphasize the role of central auditory system integrity in determining the level of functioning of DOC patients and suggest the possibility to use the ASSR protocol as an objective diagnostic method in DOC patients. (C) 2017 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.