Effects of rTMS on Brain Alterations in Stroke Patients

As the second leading cause of death and major cause of disability in the world, stroke is the rapid loss of brain function due to disturbance in the blood supply to the brain. Approximately two thirds of patients with stroke have impaired motor function even at three to six months after stroke onset. The abnormally increased interhemispheric inhibition driven from the unaffected to the affected hemisphere is associated with the motor impairment, which is characterized by increased cortical excitability in the unaffected hemisphere and decreased cortical excitability in the affected hemisphere. Rebalancing the cortical excitability between two hemispheres is associated with a better overall prognosis.

Repetitive transcranial magnetic stimulation (rTMS) is a painless, noninvasive brain stimulation technique. High-frequency rTMS facilitates cortical excitability, whereas low-frequency rTMS decreases the cortical excitability of the stimulated hemisphere. Therefore, rTMS can be used to increase and decrease the cortical excitability of the affected and unaffected hemispheres, respectively, and may facilitate motor function after stroke. However, the previous studies commonly applied behavioral scales to evaluate the effect of the rTMS treatment, little is known how the brain function and structure recover after rTMS treatment and whether the different frequency of rTMS will affect the recovery in the brain of stroke patients.

Non-invasive neuroimaging techniques provide promising avenues to detect brain function and structure in patients after stroke onset and have been increasingly applied to this disease. The morphology of the brain (cortical thickness, gray matter volume) is commonly assessed using T1-weighted MRI (Structural MRI). Diffusion tensor imaging (DTI) is a promising technique to study human brain structure, especially white matter anatomy, by providing multiple quantitative parameters to characterize tissue microstructure from different aspects. Functional magnetic resonance imaging (fMRI) is a functional neuroimaging technique which measures the changes of the blood oxygenation level-dependent (BOLD) signal that are highly correlated with neural activities. Task fMRI which applies stimulus-response pattern to identify the regions activated by performance of a cognitive task, while resting-state fMRI (rs-fMRI) is a promising tool to map intrinsic function of the human brain, which has unique advantages in clinical conditions because it does not require participants to engage in cognitive activities.

In this study, the investigators aim to evaluate functional and structural improvements in the brain of stroke patients after rTMS treatment using multi-modal MRI techniques. Specifically, the investigators sought to determine whether rTMS treatment modulate the brain function and structure in stroke patients and, if so, whether different frequency of the rTMS treatment will affect the degree of the motor recovery in patients' brain.