Stroke commonly produces an imbalance in interhemispheric functional connectivity that impedes motor recovery. The study addresses how different transcranial direct current stimulation (tDCS) montages acutely alter the lateralization of motor networks and which network shifts relate to behavioral improvement. The authors frame modulation of interhemispheric balance as a key target for neurorehabilitation interventions.
The investigation used a single-blind, randomized crossover design involving 28 patients with chronic subcortical stroke. Each participant received four interventions in separate sessions: anodal tDCS, cathodal tDCS, bilateral tDCS, and sham stimulation, all targeting the primary motor cortex. Interventions and assessments were timed to evaluate immediate, acute effects on brain network dynamics and motor behavior.
Resting-state electroencephalography (EEG) was recorded immediately before and after each stimulation session. The authors quantified network lateralization by computing dynamic functional connectivity (dFC) using mutual information and then constructing an asymmetry index matrix to capture interhemispheric differences. This approach permitted time-resolved characterization of how connectivity patterns shifted with each montage.
Key connectivity features were extracted using robust feature selection algorithms. These features were applied to classify pre- versus post-intervention network states. The selected network-dynamics features distinguished stimulation states with high accuracy: reported area under the receiver operating characteristic curve (AUC) values ranged from 0.87 to 0.98, demonstrating that the EEG-derived metrics reliably detected acute montage-specific changes.
All three active tDCS protocols produced directional modulation of network dynamics, but their mechanisms differed.
Anodal tDCS: Uniquely reversed contralesional network dominance by facilitating ipsilesional connectivity and thereby shifting the interhemispheric balance toward the affected hemisphere. This pattern indicates ipsilesional facilitation as the primary mechanism for anodal stimulation in this cohort.
Cathodal tDCS: Predominantly induced inhibition within contralesional networks rather than producing a clear ipsilesional facilitation effect.
Bilateral tDCS: Also produced contralesional network inhibition; the study highlights this inhibitory pattern as a principal effect of bilateral montage in the acute timeframe.
Sham stimulation: Showed no consistent directional bias in network lateralization.
These distinctions indicate dissociable lateralization mechanisms across montages: facilitation-driven rebalancing with anodal stimulation versus inhibition-driven change with cathodal and bilateral montages.
Behavioral outcomes were assessed acutely using the Jebsen-Taylor Hand Function Test (JTT). Among the reported findings, functional inhibition of a specific contralesional connection (P2–P6) induced by bilateral tDCS correlated significantly with acute improvements on the JTT (r = 0.55, p = 0.04). This relationship shows that particular network alterations measurable with EEG can be linked to immediate motor performance gains after stimulation.
The study provides mechanistic insight into how tDCS montages can differentially modulate post-stroke interhemispheric network dynamics. Clinically, these results suggest that montage selection could be guided by the desired direction of network modulation: use of anodal tDCS when promoting ipsilesional facilitation is preferred, and cathodal or bilateral tDCS when therapeutic strategies aim to suppress maladaptive contralesional hyperactivity. The link between a specific inhibited contralesional connection and JTT improvement supports the concept that targeted network modulation can produce measurable functional benefits.
The abstract provides the core experimental design, EEG analytic approach, classification performance (AUC range), and a specific correlation (P2–P6 connection with JTT, r = 0.55, p = 0.04). The source text does not report several details in the abstract, including exact stimulation parameters (current intensity, duration), electrode placement coordinates beyond targeting the primary motor cortex, timing between sessions, participant demographic and clinical characteristics beyond “chronic subcortical stroke,” or long-term behavioral outcomes. These specifics were not reported in the provided source abstract and would require consultation of the full text for clarification.