| A stroke, also known as cerebral apoplexy, is a disease with rapidly developing loss of brain functions due to stop or disturbance in the blood supply to the brain. 85% patients get upper limbs dysfunctional after stroke, which has very slow and difficult rehabilitation and loads heavy burden on patients themselves, their families and society. As an effective method to activate the voluntary motor networks in human neural system and improve or partially reconstruct the voluntary motor function, repeated motor imagery is both independent on remained motor function and closely related to the neural channel of voluntary movement in the patients, which has become a hot topic in the research of stroke rehabilitation. The key problem in the design and optimization of the rehabilitation protocol based on motor imagery is how to quantitatively assess the corticospinal excitability under different motor imagery patterns. Until now the relevant researches are still limited at home and abroad.In this thesis, two hand motor imagery experiments were designed based on the operation possibility and bimanual coordination of movement. At the same time, transcranial magnetic stimulation (TMS) were used to stimulate the left motor cortex of 10 subjects and the sEMG from the first dorsal interosseous(FDI) of right hand was recorded. Wavelet transform (WT) and empirical mode decomposition (EMD) were applied to remove the low-frequency drift of sEMG signals. The features of motor evoked potentials (MEP) from sEMG were extracted based on the time-locked relationship between MEP and TMS pulse to compare and analyze the corticospinal excitability which can also be called the activation level of the brain motor area under different motor imagery patterns.The results from the hand motor imagery experiment with opration possibility showed that all of the imagery tasks including both left/right and possible/impossible hand motion led to a higher MEP than the resting task, which proved that motor imagery resulted in definite non-lateral activation in the brain motor area. During the motor imagery of right hand, a significant increase in MEP was found during imagery of impossible movement in comparison with that of possible movement in all the subjects. During the motor imagery of left hand, most of the subjects (8/10) showed the similar trend. It could be concludes that both contralateral and ipsilateral imagery of impossible movement can evoke higher corticospinal excitability, which can better activate the brain motor area.The results from the hand motor imagery experiment with bimanual coordination showed that all of the imagery tasks including left hand, right hand, and bimanual coordination lead to a higher MEP than the resting task, which proved again that motor imagery resulted in definite non-lateral activation in the brain motor area; Among these three motor imagery patterns, most of the subjects (7/10) showed a significant increase in MEP during imagery of right hand than in imagery of both hands and all the subjects showed the lowest MEP during the left hand imagery, which meant that the imagery of contralateral hand brings the highest activation of the brain motor area, the second is the imagery of both hands, and the lowest is the imagery of ipsilateral hand.Above research results are expected to provide the reference and help for the optimization and design of the best motor imagery therapy protocol after stroke. In addition, it should be noticed that for some subjects in this research, their orderliness of corticospinal excitability is the opposite to that of most of the subjects, which individual differences are still need further research in the future. |
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