The Effect of Contralesional cTBS on Motor Network Activity and Connectivity in Stroke Patients Assessed with fMRI and Dynamic Causal Modeling
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Hemiparesis of the upper limb is the most common cause of disability after stroke. The exact mechanism underlying spontaneous upper limb recovery is still unclear, and more effective therapies for optimizing stroke rehabilitation are required. Following stroke, excessive inhibition from the contralesional (CL) primary motor cortex (M1) may additionally impair activation in the ipsilesional (IL) M1. This in turn may contribute to motor impairment. Continuous theta-burst stimulation (cTBS) applied over the CL M1 is believed to suppress its activation and as a result may improve motor function. The effective connectivity between both M1s can be estimated using functional magnetic resonance imaging (fMRI) and dynamic causal modeling (DCM). This study aimed to investigate the effect of cTBS applied over the CL M1 on bilateral M1 activation and effective connectivity between the M1s, and whether this correlated with motor function. Subacute stroke patients received real or sham cTBS treatment, and underwent fMRI scanning one week after treatment, and three and six months after stroke onset. Additionally, motor function tests were performed. M1 activation was assessed by the percent signal change and changes in effective connectivity were estimated by DCM of the motor network. No significant effects of real cTBS treatment on both CL M1 and IL M1 activation were found, although a trend for IL M1 activation was visible. In addition, IL M1 activation correlated positively with motor function, indicating that this might play an important role in stroke recovery. No differences in effective connectivity between bilateral M1s were found, although variability between patients was high. Taken together, more research is needed to reveal the exact role of effective connectivity between bilateral M1s in stroke recovery, and to establish the effect of cTBS applied over the CL M1 on bilateral M1 activation and effective connectivity.