Beyond the binary: excitatory rTMS of the right Broca’s Homolog in Subacute Aphasia reveals a differential spectrum of individualized neuroplastic compensation

The role of the right hemisphere in aphasia recovery remains a central debate in neurorehabilitation. While traditional paradigms often focus on a binary “excitation vs. inhibition” logic, the dynamic nature of the subacute recovery window suggests that a more nuanced, state-dependent approach is required. In this study, we investigated the efficacy and neural mechanisms of high-frequency (excitatory) repetitive transcranial magnetic stimulation (HF-rTMS) targeting the right inferior frontal gyrus in subacute post-stroke aphasia. Participants received 18 sessions of active or sham HF-rTMS over three weeks, integrated with conventional speech-language therapy. Neurophysiological evaluation was performed using functional near-infrared spectroscopy (fNIRS) during a Verbal Fluency Task (VFT) to measure task-related hemodynamic responses (ΔHbO, ΔDHb and ΔtHb) and interhemispheric dynamics at baseline and post-intervention. Active HF-rTMS yielded significantly greater gains in the Aphasia Quotient (AQ) compared to sham stimulation. Neurally, the active group exhibited a specific modulation of the right inferior frontal gyrus; however, rather than a uniform increase in excitability, we identified a “differential adaptive spectrum” consisting of both hemodynamic “increasers” and " decreasers.” These heterogeneous responses correlated with distinct behavioral recovery trajectories, suggesting that the same excitatory stimulus can facilitate different compensatory pathways depending on the individual’s baseline network state. Conclusions: High-frequency stimulation of the right inferior frontal gyrus (IFG) may support language recovery in subacute post-stroke aphasia, but the accompanying hemodynamic responses appear to differ across individuals. These findings indicate that the functional role of the right hemisphere cannot be reduced to a uniformly maladaptive or compensatory process. Accordingly, inhibitory and excitatory stimulation of the right hemisphere may not be equally appropriate for all patients. Future studies should determine whether baseline clinical and neurophysiological profiles can be used to guide more individualized selection of stimulation polarity and target.