tACS Alters EEG Microstates in DoC

Transcranial Alternating Current Stimulation Is Associated With Changes in EEG Microstate Dynamics in Disorders of Consciousness

Disorders of consciousness (DoC), including unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS), remain difficult to diagnose at the bedside. Electroencephalography (EEG) microstate analysis provides a high-temporal-resolution approach for characterizing large-scale resting-state brain dynamics, and its application in neuromodulation studies remains under investigation.

This study is designed to investigate the effects of a single 20-minute session of 40 Hz transcranial alternating current stimulation (tACS) applied over the bilateral dorsolateral prefrontal cortex (DLPFC) on resting-state EEG microstate parameters in patients with DoC. Participants undergo resting-state EEG recordings immediately before and after a 2 mA, 40 Hz bilateral DLPFC tACS session. EEG microstate maps (A-G) are identified by back-fitting to individual recordings, and microstate parameters including mean duration, occurrence, coverage, and global explained variance (GEV) are calculated. Behavioral assessments are performed using the Coma Recovery Scale-Revised (CRS-R) and the Simplified Evaluation of CONsciousness Disorders (SECONDs). The study aims to characterize changes in EEG microstate dynamics following tACS and to examine their associations with behavioral measures of consciousness.

Inclusion Criteria:

• Adults aged 18 years or older.
• Medically stable at the time of assessment.
• No administration of sedative or hypnotic medication within the previous 24 hours.
• Preserved wakefulness (spontaneous or elicited by stimulation) with reduced or absent awareness, consistent with Unresponsive Wakefulness Syndrome (UWS) or Minimally Conscious State (MCS).
• Diagnosis confirmed by an experienced neurologist using repeated clinical assessments with the Coma Recovery Scale-Revised (CRS-R) and the Simplified Evaluation of CONsciousness Disorders (SECONDs) performed on different days and at different times during periods of wakefulness.

Exclusion Criteria:

• Acute phase of brain injury (within the first 28 days after injury).
• Administration of sedative or hypnotic medication within the previous 24 hours.
• Medical instability (e.g., active infection or hemodynamic instability).
• Epileptic seizures uncontrolled despite anticonvulsant therapy.
• Serious systemic illnesses that could affect the level of consciousness (e.g., sepsis or end-stage organ failure).
• Brain death or coma without any evidence of wakefulness.
• A previous history of developmental disorders, major neurological disorders, or severe psychiatric disorders associated with significant functional impairment.