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

## TL;DR

This study finds that chronic stroke patients show reduced frontal midline theta brain activity during a cognitive task compared to healthy older adults, using MEG data.

## Contribution

The study explores task-induced frontal midline theta activity in chronic stroke patients using MEG source localization, revealing differences in cognitive control mechanisms.

## Key findings

- Healthy older adults showed significant frontal midline theta clusters near ACC/mPFC during a Go/NoGo task.
- Stroke patients exhibited lower baseline and task-related theta power compared to healthy controls.
- Localization of theta sources in stroke patients was more variable and less consistent.

## Abstract

•MEG data were recorded from stroke patients and healthy older adults during Go/NoGo.•Theta sources were localized close to ACC/mPFC.•Preliminary results indicate reduced frontal midline theta in chronic stroke.•Effect seems driven by lower theta power at baseline and after NoGo stimuli.•Challenges in localizing Theta sources in stroke patients are discussed.

MEG data were recorded from stroke patients and healthy older adults during Go/NoGo.

Theta sources were localized close to ACC/mPFC.

Preliminary results indicate reduced frontal midline theta in chronic stroke.

Effect seems driven by lower theta power at baseline and after NoGo stimuli.

Challenges in localizing Theta sources in stroke patients are discussed.

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.