Immediate Aftereffect of tACS on Directed Functional Brain Networks in Subacute Stroke Patients

Transcranial alternating current stimulation (tACS) can modulate endogenous oscillations in the brain by inducing neural plasticity and is considered beneficial for the restoration of brain function. However, its neuromodulatory effects in stroke patients still require further investigation. This study investigated the immediate modulatory aftereffect impact of 20 Hz tACS on multi-band functional brain networks in subacute stroke patients. Thirteen patients underwent resting-state electroencephalogram (EEG) recordings before and after stimulation. Directed functional brain networks across five frequency bands were constructed using phase transfer entropy (PTE) to assess global and local efficiency, directed connection density, and inter-regional information flow. Results revealed that tACS significantly enhanced global efficiency in low-frequency (delta, theta) networks while reducing local efficiency in high-frequency (alpha, beta, gamma) networks ( ${p}\lt 0.05$ ). Following tACS, five frequency bands networks all exhibited a significant increase in information flow from the contralesional to ipsilesional hemisphere ( ${p}\lt 0.05$ ). Moreover, information flow from the contralesional to ipsilesional hemisphere significantly increased across all bands, accompanied by a role shift of key parietal, temporal, and occipital regions between information sources and sinks. These findings demonstrate that 20 Hz tACS can rapidly reorganize cross-frequency, cross-hemisphere, and cross-regional information transmission, providing evidence for its potential to modulate neural dynamics and support functional recovery in stroke rehabilitation.