Electroencephalography Markers of Brain Stimulation in Post-Concussion Patients (Stim-PPCS)

Active tDCS participants will receive high-definition cerebellar transcranial direct current stimulation using a multi-electrode montage optimized to target bilateral cerebellar regions. The electrode configuration is identical across conditions and has been defined using computational modeling to maximize focality while limiting current spread to adjacent areas. The stimulation consists of a 30-second ramp-up phase, followed by 20 minutes of continuous stimulation, and a 30-second ramp-down phase.

Transcranial direct current stimulation is a non-invasive brain stimulation technique that delivers a weak direct electrical current through scalp electrodes to modulate neuronal excitability (<2mA). Cerebellar tDCS will be administered using an 8-channel montage optimized with the Stimweaver software (Neuroelectrics, Barcelona, Spain) to maximize current density over the cerebellum while minimizing off-target effects. A constant direct current will be applied for 20 minutes, with a 30-second ramp-up at the beginning and a 30-second ramp-down at the end. Other Name:

Sham tDCS participants will undergo the same high-definition cerebellar electrode montage as the active tDCS group, ensuring identical setup and participant experience. However, no sustained current is delivered to the scalp. The protocol includes brief ramp-up and ramp-down phases at the beginning and end of the session to mimic the sensations of real stimulation, while preventing any meaningful modulation of cortical excitability. This approach, established in previous studies, maintains blinding of participants to the stimulation condition. The investigator administering the stimulation will also be blinded, as the tDCS device allows double blinding, with identical screen displays in both sham and active conditions.

Transcranial direct current stimulation is a non-invasive brain stimulation technique that delivers a weak direct electrical current through scalp electrodes to modulate neuronal excitability (<2 mA). The device used has a sham setting that allows sham stimulation to be delivered while the interventionist remains blinded.Other Name:

EEG functional connectivity will be assessed using the debiased weighted Phase Lag Index (dwPLI) in the alpha frequency band (8-12 Hz). This metric quantifies the consistency of phase relationships between EEG signals across brain regions while minimizing the effects of volume conduction. It will be used to evaluate changes in large-scale brain network connectivity associated with cerebellar transcranial direct current stimulation (tDCS) in patients with persistent post-concussion symptoms (PPCS). Differences in connectivity patterns between pre- and post-stimulation recordings, as well as between active and sham groups, will be analyzed.

Permutation Entropy (PE) will be calculated from EEG signals to quantify the temporal irregularity and unpredictability of brain activity. PE is a dimensionless measure.

Normalized Lempel-Ziv Complexity (LZC) will be calculated from EEG signals to quantify the diversity and complexity of brain activity patterns. LZC is a dimensionless measure.

EEG microstate analysis will be conducted to examine temporal dynamics of large-scale brain networks. Metrics will include microstate duration, coverage, and occurrence. These will be computed from resting-state EEG recordings acquired before and after stimulation to explore modulation of brain network organization.

Spectral properties of EEG signals will be analyzed, including alpha peak frequency and spectral slope. These measures provide insight into oscillatory activity and excitation-inhibition balance. Analyses will be performed on resting-state EEG recordings collected pre- and post-intervention.

Analyses will assess phase-amplitude coupling and coherence to evaluate cross-frequency interactions and synchronization between brain regions. These measures will be derived from resting-state EEG recordings before and after stimulation.

The participation coefficient in the alpha band will be computed to assess the integration of brain regions within large-scale networks. This will be derived from resting-state EEG data collected pre- and post-intervention.

Post-concussion symptoms will be assessed using the French version of the Rivermead Post-Concussion Symptoms Questionnaire (total score range: 0-64, with higher scores indicating greater symptom severity). This self-reported measure evaluates the severity of common post-concussion symptoms and will be used to characterize baseline symptom burden.

Participants will complete a computerized simple reaction time task to assess processing speed and motor responsiveness. Performance will be compared before and after stimulation.

The SCAT6 symptom evaluation (Step 2) will be used to assess immediate concussion-related symptoms (total score range: 0-132, with higher scores indicating greater symptom severity). This questionnaire will be administered before and after the intervention to explore changes in symptom severity.

A computerized cognitive task assessing attention will be administered pre- and post-intervention. Performance metrics will be analyzed to evaluate potential cognitive effects of the stimulation.

A blinding questionnaire will be completed by both the participant and the interventionist to assess the effectiveness of blinding between active and sham stimulation conditions.

Adverse events will be assessed using a standardized questionnaire as described in Reckow et al. This will capture any discomfort or side effects associated with the intervention.

Sociodemographic data will be collected to characterize the study population, including age, gender, level of education, employment status, physical activity level, and substance use (alcohol, tobacco, and drugs). Participants' medical history and current medication use will be recorded to characterize baseline health status and control for potential confounding factors in analyses.