Inter-hemispheric coupling changes associate with motor improvements after robotic stroke rehabilitation

Purpose: In the chronic phase of stroke brain plasticity plays a crucial role for further motor control improvements. This study aims to assess the brain plastic reorganizations and their association with clinical progresses induced by a robot-aided rehabilitation program in chronic stroke patients. Methods: 7 stroke patients with an upper limb motor impairment in chronic phase underwent a multi-modal evaluation before starting and at the end of a 12-week upper-limb neurorehabilitation program. Fugl-Meyer Assessment (FMA) Scale scores and performance indices of hand movement performance (isometric pinch monitored through a visual feedback) were collected. Cerebral reorganizations were characterized by 32-channel electroencephalography (EEG) focusing on ipsilesional and contralesional resting state properties investigating both bipolar derivations overlying the middle cerebral artery territory and the primary somatosensory sources (S1) obtained through the Functional Source Separation (FSS) method. Power Spectral Density (PSD) and interhemispheric coherence (IHCoh) at rest were measured and correlated with clinical and hand control robot-induced improvements. Results: After the robotic rehabilitation we found an improvement of FMAS scores and hand motor control performance and changes of brain connectivity in high frequency rhythms (24-90 Hz). In particular, the improvement of motor performance correlated with the modulation of the interhemispheric S1 coherence in the high beta band (24-33 Hz). Conclusions: Recently it has been shown that an upper limb robot-based rehabilitation improves motor performance in stroke patients. We confirm this potential and demonstrate that a robot-aided rehabilitation program induces brain reorganizations. Specifically, interhemispheric connectivity between primary somatosensory areas got closer to a 'physiological level' in parallel with the acquisition of more accurate hand control.