Interaction between Cortical Blood Flow and Muscle Activation during Isometric Contraction of Paretic Elbow Flexor and Extensor in Stroke Survivors: A Preliminary Study

Upper limb motor dysfunction is common in stroke survivors but the mechanism behind the impairment is still poorly understand. The correlation between the performance of motor task and brain activity in patients after stroke is warrant to investigate. In this current study, functional Near-infrared Spectroscopy (fNIRS) and surface electromyography (sEMG) were used to study the relationship between brain region activation and peripheral muscle contraction in different motor control tasks, and to explore the changes of information transmission between cerebral cortex and peripheral muscle in stroke patients. Three stroke patients were recruited and asked to perform elbow isometric flexion and extension on the affected side and unaffected sides. Blood oxygen concentrations in brain from fNIRS and sEMG signals in the biceps brachii (BIC) and triceps brachii (TRI) muscles were recorded simultaneously during different isometric contraction levels. Cortical activation and functional connectivity were used to measure information interaction in brain activity and the variation of elbow contraction under different exercise tasks was analyzed by root mean square (RMS) and co-contraction index (CCI) from sEMG signals. It was found that the RMS of the BIC and TRI on the unaffected side was greater than that on the affected side during both elbow isometric flexion and extension tasks. Meanwhile, in the 30% MVC condition, the CCI of the unaffected side of elbow isometric flexion and extension was lower than that of the affected side. The results showed that the activation of brain regions on the ipsilateral side was higher than that on the contralateral side, especially the motor cortex and the prefrontal cortex. Meanwhile, the results of functional connectivity were lower from ipsilateral than those on the contralateral side. In this study, the changes of blood oxygen in the brain and the changes of sEMG signal have a same trend of synchronization during motor tasks. This finding provides a basis for further exploration of the mapping relationship between brain activity and motor task performance in stroke patients, and can guide the rehabilitation intervention of motor function in stroke survivors.