Evoked slow oscillations and dynamic network reorganization after stroke

A focal ischemic lesion is thought to alter neuronal activity beyond the area of structural damage, thereby interfering with the whole network architecture. Here, we used a combination of transcranial magnetic stimulation and electroencephalography in conjunction with dynamic connectivity analyses and graph theory to study alterations and reorganization of cortical connectivity in a cohort of 41 patients longitudinally after stroke. We found a link between an increase in low-frequency coupling in the delta band and alterations in neural information processing in the first weeks after stroke and their relevance for motor outcome >3 months later. We demonstrated that stroke enhances slow activity and delta coupling between frontocentral and parietal regions. In addition, we observed a loss of the physiological network architecture with a decrease in small-worldness and modularity in the delta frequency, implying that a focal ischemic lesion interferes with both cortical information integration and functional segregation within the first weeks after stroke. While we found a link between bifrontal coupling in the alpha spectrum and the degree of the motor deficit in the early post-acute phase, the amount of small-worldness disruption early after stroke indicated the motor outcome in the follow-up session. In contrast, recovery of motor function and cortical reorganization after >3 months post-stroke were paralleled by the normalization of increased low-frequency coupling and a reinstatement of the complex network structure featuring a modular and small-world topology.