Review Maps EEG Markers of tDCS Effects in Post-Stroke Motor Recovery

A narrative review published ahead of print in Clinical EEG and Neuroscience surveys how scalp electroencephalography (EEG) captures brain activity changes induced by transcranial direct current stimulation (tDCS) during post-stroke motor recovery. The review organizes the evidence around four families of EEG measures: power spectral density (PSD, the distribution of oscillatory power across frequency bands), functional connectivity between recording sites, the brain symmetry index (BSI, a scalar quantifyininterhemispheric asymmetry), and event-related brain responses.

The subject population is stroke survivors undergoing motor rehabilitation, a cohort in which tDCS is widely applied as an adjunct to physiotherapy. The modality under review is scalp EEG, not intracranial or ECoG recording, which matters for reading rooms and rehabilitation labs interpreting the cited literature.

What does the review change for clinical practice?

For neurophysiologists and rehabilitation clinicians, the practical value lies in consolidation. Rather than a single trial, the authors assemble the EEG literature on tDCS effects into a framework organized by measure. Readers who monitor or report EEG in stroke recovery can use this framework to anticipate which quantifiers — spectral power, connectivity metrics, BSI, event-related responses — have been applied to stimulation studies and what each is intended to detect.

The review is narrative rather than systematic or meta-analytic. It does not report a pooled effect size, and it should be read as a synthesis of the literature rather than as a trial with its own cohort. No device in this context is presented as FDA-cleared for the specific indication reviewed; tDCS effects on post-stroke motor recovery remain an active research field, and the EEG measures discussed are investigational correlates of those effects.

Which EEG measures are at the center?

The review's structure names four quantifiable windows on stimulation-induced change:

• Power spectral density, indexing band-specific changes in cortical oscillations after stimulation sessions.
• Functional connectivity, characterizing altered coupling between scalp electrodes and between hemispheres.
• The brain symmetry index, a measure designed to summarize the pathological interhemispheric imbalance that follows stroke and that rehabilitation aims to reduce.
• Event-related brain responses, time-locked electrophysiological signatures of motor and cognitive processing.

Each measure carries distinct acquisition and analysis demands. PSD and connectivity derive from resting-state or task recordings and require careful reference and artifact handling. BSI presupposes a standardized montage supporting left-right comparison. Event-related responses require repeated time-locked trials, typically during motor tasks.

How should readers weigh the evidence?

Because the article is ahead of print and narrative in design, its contribution is interpretive: it maps which EEG endpoints have been used to track tDCS-induced physiological change in stroke motor recovery and how they relate to behavioral outcome. It does not establish new clinical indications. Clinicians running neurophysiology labs alongside rehabilitation services can treat the four-measure framework as a checklist when designing monitoring protocols or when reading stimulation studies critically.

The distinction between investigational correlates and validated biomarkers remains consequential. EEG changes under tDCS, as the review frames them, are physiological observations whose clinical predictive value in post-stroke motor recovery continues to be established.

Going forward, the review sets the stage for prospective studies that pair standardized scalp EEG quantification — PSD, connectivity, BSI and event-related responses — with controlled tDCS dosing in defined stroke populations, work that could determine whether any of these measures can serve as reliable readouts of stimulation response.