Reduced task-induced frontal midline theta activity in chronic stroke patients compared to healthy older adults - An MEG study.

Frontal midline theta (FMΘ) is a well-established neural marker of cognitive control, generated predominantly in the anterior cingulate cortex (ACC). While reduced theta power has been reported in stroke using EEG, little is known about task-induced FMΘ and its sources in healthy older adults and stroke patients. Understanding FMΘ dynamics is crucial for characterizing post-stroke changes in the neural mechanisms underlying cognitive control and may aid the development of targeted neuromodulation approaches. In this exploratory study, seventeen healthy older adults and ten chronic ischemic stroke patients performed a Go/NoGo task during magnetoencephalography (MEG). MEG signals were projected into source space using an LCMV beamformer, allowing to localize sources of task-induced FMΘ. At the group level, healthy older adults showed a significant FMΘ cluster localized near the ACC and medial prefrontal cortex. Region-of-interest analyses revealed that healthy older adults exhibited significantly greater task-related FMΘ compared to stroke patients and overall higher baseline theta activity, suggesting impaired upregulation of FMΘ in the patient group during cognitive control. Overall, the results demonstrate that MEG source localization can capture task-induced FMΘ in healthy older adults at the group level, while modulation in stroke patients appeared more variable and less consistent. Reliable individual localization proved challenging in both groups, suggesting that group-level profiles may currently provide a more feasible basis for stimulation target definition in post-stroke rehabilitation. Future work should focus on validating these findings in larger and more heterogeneous stroke cohorts and on developing methods to bridge the gap between group-level markers and individualized neuromodulation approaches.