Association of TMS-EEG interhemispheric imbalance with upper limb motor impairment in chronic stroke patients: An exploratory study

Objective

The involvement of interhemispheric cortical dynamics in the recovery of upper limb (UL) motor functions in chronic stroke patients was investigated using combined transcranial magnetic stimulation and electroencephalography (TMS-EEG).

Methods

Ten patients with a history of single ischemic chronic stroke were enrolled (4F, 63.8?±?9.9?years).

Each patient underwent TMS-EEG recordings to evaluate interhemispheric cortical dynamics as well as a reaching task recorded with inertial measurement units, and a series of clinical assessments.

TMS-EEG neurophysiological data were analysed considering spatiotemporal, power response, and interhemispheric balance (IHB) dynamics.

Results

It was found that the IHB index (IHBi) and low-frequency power (LFP) (4–13 Hz) in the affected hemisphere were associated with the degree of UL impairment.

Conclusion

Increased IHBi due to stroke is an unfavourable factor of UL’ functions.

Similarly, LFP of both hemispheres is strongly correlated with clinical and kinematic outcomes.

Significance

TMS-EEG biomarkers of interhemispheric unbalance could be used to estimate functional recovery and drive tailored neuromodulation and neurorehabilitation approaches.

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Martino Cinnera A, Casula EP, Pezzopane V, D'Acunto A, Maiella M, Bonnì S, Ferraresi M, Guacci M, Tramontano M, Iosa M, Paolucci S, Morone G, Vannozzi G, Koch G. Association of TMS-EEG interhemispheric imbalance with upper limb motor impairment in chronic stroke patients: An exploratory study. Clin Neurophysiol. 2025 Jan 20;171:95-106. doi: 10.1016/j.clinph.2024.12.027.

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Section snippets

Participants and study design

A group of 42 patients with a history of first‐ever unilateral chronic ischemic stroke (> 180?days) (Kwakkel et al., 2023), with moderate-to-severe hemiparesis affecting UL and without contraindications for TMS, were screened for inclusion in this study. Of the twelve patients included in the study, ten right-handed patients successfully completed all assessment procedures (63.8?±?9.9?years; 4F) (complete demographic and clinical characteristics are available in Table 1). This sample size …

Results

The entire procedure was generally well tolerated by the participants. Only one patient reported a single episode of slight headache resolved without drug intervention in a few minutes after stimulation. Ten out of twelve enrolled patients completed all the evaluations (clinical, neurophysiological and kinematics). One patient dropped out for personal reasons, and the other did not perform a kinematic evaluation due to a sensor failure. Among the investigated variables, the IHBi, ISP(AHs), ISP …

Discussion

Using TMS-EEG, we found that chronic stroke patients show an imbalance in the signal transmission between the two M1 areas, which is associated with poor motor recovery. Moreover, TMS of the AH induced a higher response in terms of LFP (4–13?Hz). The correlations of IHBi and LFP with clinical and kinematics individual scores confirmed their role in estimation of UL functionality. In line with previous investigations, our results support the involvement of IHB in driving motor recovery after …

Conclusion

Our results support the hypothesis that interhemispheric imbalance plays a role in motor function recovery in chronic stroke. Patients with higher IHBi, driven by the AH, showed poor motor recovery compared to patients with rebalanced activity of the two hemispheres. Furthermore, chronic patients showing a higher IHBi, and higher theta-alpha expression (in the perilesional motor areas) are associated with a limited motor recovery imputable to a maladaptive plasticity phenomenon. Interestingly, …

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