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

• Main Authors: Bonnì, S. (Author), Borghi, I. (Author), Bozzali, M. (Author), Caltagirone, C. (Author), Casula, E.P (Author), Giulietti, G. (Author), Koch, G. (Author), Maiella, M. (Author), Martino Cinnera, A. (Author), Pellicciari, M.C (Author), Ponzo, V. (Author), Rocchi, L. (Author), Sallustio, F. (Author), Salsano, I. (Author), Spanò, B. (Author)
• Format: Article
• Language: English
• Published: John Wiley and Sons Inc 2021
• Subjects: adult; Adult; aged; Aged; antidepressant agent; Article; baclofen; benzodiazepine derivative; brain cortex; brain ischemia; cerebral artery disease; Cerebral Cortex; cerebrovascular accident; clinical article; comparative study; connectome; Connectome; controlled study; electroencephalography; Electroencephalography; Evoked Potentials, Motor; eye movement; female; Female; fractional anisotropy; hand; Hand; hand strength; human; Humans; Infarction, Middle Cerebral Artery; interhemispheric dynamics; interhemispheric transfer; Magnetic Resonance Imaging; male; Male; mean diffusivity; middle aged; Middle Aged; middle cerebral artery; Morlet wavelet transform; motor evoked potential; muscle contraction; neurophysiology; nuclear magnetic resonance imaging; pathophysiology; physiology; pinch strength; priority journal; pyramidal tract; Pyramidal Tracts; stroke; Stroke; stroke patient; transcranial magnetic stimulation; Transcranial Magnetic Stimulation
• Online Access: View Fulltext in Publisher

 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 hand strength were the ones with a more stable interhemispheric balance. Finally, we found an association between microstructural integrity of callosal fibers, suppression of interhemispheric TMS-evoked activity and interhemispheric connectivity. We provide direct and sensitive cortical measures of interhemispheric imbalance in stroke patients. These measures offer a reliable means of distinguishing healthy and pathological interhemispheric dynamics. © 2020 The Authors. Human Brain Mapping published by Wiley Periodicals LLC.