Phase Property of Envelope-Tracking EEG Response is Preserved in Patients with Disorders of Consciousness.

Abstract

When listening to speech, the low-frequency cortical response below 10 Hz can track the speech envelope. Previous studies have demonstrated that the phase lag between speech envelope and cortical response can reflect the mechanism by which the envelope-tracking response is generated. Here, we analyze whether the mechanism to generate the envelope-tracking response is modulated by the level of consciousness, by studying how the stimulus-response phase lag is modulated by the Disorder of Consciousness (DoC). It is observed that DoC patients in general show less reliable neural tracking of speech. Nevertheless, the stimulus-response phase lag changes linearly with frequency between 3.5 and 8 Hz, for DoC patients who show reliable cortical tracking to speech, regardless of the consciousness state. The mean phase lag is also consistent across these DoC patients. These results suggest that the envelope-tracking response to speech can be generated by an automatic process that is barely modulated by the consciousness state.Significance StatementDuring speech listening, a prominent cortical response is the speech envelope-tracking activity. In the frequency domain, the two fundamental characteristics of envelope-tracking activity are power and phase. Recent studies have demonstrated that the phase property of envelope-tracking activity can reveal its underlying generation mechanism. In this study, we investigate whether this generation mechanism is modulated by the state of consciousness. We introduce healthy individuals and patients with disorders of consciousness. Results demonstrate that the stimulus-response phase lag changes linearly with frequency for both healthy individuals and patients who exhibit reliable neural tracking of the speech envelope. Thus, envelope-tracking activity is generated through an automatic process, which is not strongly modulated by the state of consciousness.