Evidence for interhemispheric imbalance in stroke patients as revealed by combining transcranial magnetic stimulation and electroencephalography

Abstract

Interhemispheric interactions in stroke patients are frequently characterized by abnormalities, in terms of balance and inhibition. Previous results showed an impressive variability, mostly given to the instability of motor-evoked potentials when evoked from the affected hemisphere. We aim to find reliable interhemispheric measures in stroke patients with a not-evocable motor-evoked potential from the affected hemisphere, by combining transcranial magnetic stimulation (TMS) and electroencephalography. Ninteen stroke patients (seven females; 61.26 ± 9.8 years) were studied for 6 months after a first-ever stroke in the middle cerebral artery territory. Patients underwent four evaluations: clinical, cortical, corticospinal, and structural. To test the reliability of our measures, the evaluations were repeated after 3 weeks. To test the sensitivity, 14 age-matched healthy controls were compared to stroke patients. In stroke patients, stimulation of the affected hemisphere did not result in any inhibition onto the unaffected. The stimulation of the unaffected hemisphere revealed a preservation of the inhibition mechanism onto the affected. This resulted in a remarkable interhemispheric imbalance, whereas this mechanism was steadily symmetric in healthy controls. This result was stable when cortical evaluation was repeated after 3 weeks. Importantly, patients with a better recovery of the affected

Intermittent Theta Burst Stimulation Increases Natural Oscillatory Frequency in Ipsilesional Motor Cortex Post-Stroke: A Transcranial Magnetic Stimulation and Electroencephalography Study

“…Furthermore, MEPs reflect cortical excitability in only motor cortex but not non-motor brain regions. Concurrent use of TMS and electroencephalography (EEG) (i.e., TMS-EEG) would overcome the drawbacks of MEP measurements, which offers a chance to simultaneously monitor cortical activity in both stimulated area and the interconnected cortical networks ( Casula et al, 2021 ). Importantly, as TMS-EEG can directly measure cortical reactivity and oscillatory dynamics regardless of the integrity of corticospinal tracts ( Borich et al, 2016 ), it allows for investigating neural effects induced by iTBS in stroke survivors without recordable MEPs ( Pellicciari et al, 2018 ).…”

Impact of interhemispheric inhibition on bimanual movement control in young and old

“…Thus, the inconsistency could also derive from the potential asymmetry of S-IHI and its association with mirror activity. According to a recent study showing functional relevance of the symmetry of interhemispheric propagation for stroke patients (Casula et al 2021 ), the potential symmetry/asymmetry of IHI and its association with bimanual movement control have to be addressed in more detail in upcoming studies. Nevertheless, the degree of S-IHI rest could still represent behavioral relevance for bimanual movement control (Hübers et al 2008 ; Wahl et al 2016 ).…”

Electroencephalogram (EEG) With or Without Transcranial Magnetic Stimulation (TMS) as Biomarkers for Post-stroke Recovery: A Narrative Review

“…In a study in which interhemispheric functional connectivity in EEG was not apparent at rest, TEPs were used to unmask interhemispheric functional connectivity in chronic stroke patients ( 117 ). Casula et al observed that single-pulse TMS pulses on contralesional created a significant interhemispheric imbalance, which led to suppression of the activity in the lesioned hemisphere ( 123 ). Furthermore, patients who later experienced a better recovery showed more balanced TMS-evoked activity between hemispheres.…”