Towards an electroencephalographic measure of awareness based on the reactivity of oscillatory macrostates to hearing a subject's own name

• Published in: The European journal of neuroscience Vol. 59; no. 5; pp. 771 - 785
• Main Authors: Șerban, Cosmin‐Andrei, Barborică, Andrei, Roceanu, Adina‐Maria, Mîndruță, Ioana‐Raluca, Ciurea, Jan, Stancu, Mihai, Pâslaru, Alexandru C., Zăgrean, Ana‐Maria, Zăgrean, Leon, Moldovan, Mihai
• Format: Journal Article
• Language: English
• Published: France Wiley Subscription Services, Inc 01.03.2024
• Subjects: (un)consciousness; brain oscillations; clinical neurophysiology; Coma; Cortex (cingulate); EEG; Electroencephalography; Glasgow Coma Scale; Ischemia; Somatosensory cortex; stroke; brain oscillations; (un)consciousness; clinical neurophysiology; stroke; coma
• ISSN: 0953-816X; 1460-9568; 1460-9568
• DOI: 10.1111/ejn.16138

We proposed that the brain's electrical activity is composed of a sequence of alternating states with repeating topographic spectral distributions on scalp electroencephalogram (EEG), referred to as oscillatory macrostates. The macrostate showing the largest decrease in the probability of occurrence, measured as a percentage (reactivity), during sensory stimulation was labelled as the default EEG macrostate (DEM). This study aimed to assess the influence of awareness on DEM reactivity (DER). We included 11 middle cerebral artery ischaemic stroke patients with impaired awareness having a median Glasgow Coma Scale (GCS) of 6/15 and a group of 11 matched healthy controls. EEG recordings were carried out during auditory 1 min stimulation epochs repeating either the subject's own name (SON) or the SON in reverse (rSON). The DEM was identified across three SON epochs alternating with three rSON epochs. Compared with the patients, the DEM of controls contained more posterior theta activity reflecting source dipoles that could be mapped in the posterior cingulate cortex. The DER was measured from the 1 min quiet baseline preceding each stimulation epoch. The difference in mean DER between the SON and rSON epochs was measured by the salient EEG reactivity (SER) theoretically ranging from −100% to 100%. The SER was 12.4 ± 2.7% (Mean ± standard error of the mean) in controls and only 1.3 ± 1.9% in the patient group (P < 0.01). The patient SER decreased with the Glasgow Coma Scale. Our data suggest that awareness increases DER to SON as measured by SER. We recorded the EEG during repetitive auditory stimulation with either the subject's own name (SON) or its reverse (rSON) in a group of post‐stroke patients with impaired awareness. We identified the default EEG macrostate (DEM) by its reoccurring topographic spectral features and its reactivity, defined as the reduction in its occurrence probability during stimulation. In the patients, the difference in DEM reactivity between SON and rSON stimulation decreased with the Glasgow Coma Scale score.