tACS Alters EEG Microstates in DoC

Istanbul Medipol University Hospital31 enrolled

Overview

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.

Study Type

INTERVENTIONAL

Allocation

Purpose

TREATMENT

Masking

NONE

Enrollment

Conditions

Disorder of Consciousness

Transcranial Alternating Current StimulationDEVICE

After completion of the first 20-minute resting-state EEG, tACS was applied using a Neurosoft / Neurostim device. Stimulation was performed at the 40 Hz gamma frequency, with two stimulation electrodes placed bilaterally over the DLPFC. According to the international 10-20 system, this placement corresponded to the F3 (left DLPFC) and F4 (right DLPFC) electrode positions. The stimulation lasted 20 minutes, and a constant current intensity of 2 mA was used throughout. The current was delivered as a sinusoidal waveform without phase shifting or modulation. The electrodes were sponge-based pads measuring 5 × 7 cm each. To improve conductivity and ensure homogeneous skin contact, the sponge electrodes were moistened with 0.9% isotonic sodium chloride (saline). Electrodes were secured to the skin to optimize contact quality and homogenize current distribution.

Eligibility

Sex: ALLMin age: 18 Years

Medical Language ↔ Plain English

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.

Outcomes

Primary Outcomes

Resting-State EEG Microstate Parameters

EEG recordings were obtained in different settings according to the patient's physical condition. From every individual, a total of 20 minutes of resting-state EEG was obtained. EEG recordings were performed using a Neurosoft NEURON-SPECTRUM-4 device and Neuron-Spectrum.NET software. Recordings were obtained from 19 electrode channels positioned according to the international 10-20 system: Fp1, Fp2, F7, F3, Fz, F4, F8, T7, C3, Cz, C4, T8, P7, P3, Pz, P4, P8, O1, O2. Data were digitized at a sampling rate of 500 Hz. Resting-state electroencephalography (EEG) microstate parameters, including mean duration, occurrence, coverage, and global explained variance (GEV) of microstate classes A-G, derived from 19-channel scalp EEG recordings using microstate analysis.

Time frame: Baseline and immediately after the 20-minute tACS session.

Coma Recovery Scale-Revised (CRS-R)

The CRS-R is a standardized clinical assessment tool used to evaluate the level of consciousness in patients with disorders of consciousness. It consists of six subscales: auditory, visual, motor, oromotor/verbal, communication, and arousal. The total score ranges from 0 to 23, with higher scores indicating a higher level of consciousness. Diagnostic interpretation is based not only on the total score but also on the highest behavioral responses observed within each subscale.

Time frame: Baseline and immediately after the 20-minute tACS session.

Simplified Evaluation of CONsciousness Disorders (SECONDs)

The SECONDs is a brief bedside assessment designed for the rapid evaluation of patients with disorders of consciousness. It assesses arousal and behavioral responses to simple commands and environmental stimuli. The total score ranges from 0 to 8, with higher scores indicating a better level of consciousness. It is a practical tool for screening and longitudinal clinical monitoring.

Time frame: Baseline and immediately after the 20-minute tACS session.

tACS Alters EEG Microstates in DoC

Overview

Conditions

Interventions

Eligibility

Locations (1)

Outcomes

Primary Outcomes