| The brain function of motor system mainly involves either the motor execution (ME), which refers to the overt body movement to finish certain task, or the motor imagery (MI), which refers to the mental rehearsl of motor movement without any overt body movement. It is not only the theoretical principle of brain computer interface (BCI), but also the significant field of brain function research. It has been demonstrated to play a very important role in training for athletes and musicians, and also in the recovery of motor abilities in patients with movement disorders. The researches on the brain function of motor system currently focus on the functional magnetic resonance imaging (fMRI) experiment, the location of the brain function and the relationship between the functional regions of the brain, lacking the study on the dynamic networks of the brain function, especially the quantitative analyses and evaluation of the dynamic networks.The present dissertation focused on the neural mechamism of brain function of motor system, using related research methods and mathematic models to study the functional networks of the motor system of human brain, as well as the connective relations among the networks. Based on hand movement-related fMRI experiments, the functional asymmetry in motor areas and sub-cortical structures related to handedness, the effective connectivity networks of the motor system during both ME and MI, and the comparison of the dynamic brain networks between ME and MI were accomplished. The details are as follows:1. The Gaussian convolution model approach was applied to the fMRI signal acquired during sequential finger movements of the left- and right-handed subjects, to systematically and quantitatively investigated asymmetry in primary motor cortices (M1) in temporal domain. Our results showed that regardless of handedness and bi- or uni-manual movement, it took the dominant hand a longer average interval of response delay and a more variable standard deviation than those of the non-dominant hand to perform movements. Furthermore, when comparing bi-manual with uni-manual movement conditions, both of the parameters of the Gaussian function were significantly smaller in the bi-manual condition, showing that the movement of the non-dominant hand influenced that of the dominant hand. Our results extended the conclusion of the asymmetry in motor areas in right- or left-handed people from spatial domain to temporal domain, showing that the Gaussian model has the ability to evaluate this asymmetry in temporal domain.2. The fMRI signal was used to study the influence of the handedness on the brain function, by comparing the coordinates of the peak activation in M1 and cerebellum (CRB) during bi-manual and uni-manual movement. The results showed that in M1 there was no significant difference in the site of peak activation and the site was insensitive to the handedness, implying that the handedness representation in M1 was not manifested in the site but in the intensity and cluster size. However, the results showed the significantly different coordinate in CRB comparing the right-handed with the left-handed subjects both during bi-manual and uni-manual movement. Our study implied that the lateralization in CRB is ipsilateral, and extended the conclusion to the left handedness.3. The Granger causality (GC) analysis was used to detect the effective connectivity between the activated voxels in the left M1 and other parts of the brain. By choosing the left M1 as a reference region, the fMRI signal of the right-handed subjects performing a classic bimanual movement was analized to study the dynamic function networks of the whole brain and the sub-cortical structure. The result extended the conclusion of previous work that the left M1 plays a prominent role in finger movement to the conclusion in the Granger causality sense. Also, the results demonstrated the information transinformation of the bilateral M1 during bi-manual movements. As for supplementary motor ares (SMA), the results showed a statistically significant causal connectivity with the left M1 during manual movement, which confirmed that the left SMA is the'cause'and has a dominant role over the left M1 in right-handed subjects. Forthermore, the results of the group analysis confirmed the influence of the vermis and CRB over the left M1 during bimanual movement and extended these findings to a larger number of human subjects.4. The conditional Granger causality (CGC) method was used to address the pseudo Granger causality problem, and was applied to explore the effective connectivity networks of brain during dominant/nondominant hand ME and MI based on fMRI data. Selecting contralateral M1, bilateral SMA and dorsal premotor cortex (PMd) as regions of interest, the results demonstrated more closed-loop circuit of effective connectivity during right-hand performance than during left-hand performance, and more effective connections during ME than during MI. We further found that regardless of right-/left-hand performance and ME/MI condition, the closed-loop circuit between SMA and M1 was specifically located in the contralateral hemisphere, and information interchanges between PMd and SMA occurred mainly in the same hemisphere. More particularly, left PMd was found to have direct effects on both right M1 and right PMd instead of affecting right M1 via right PMd during the tasks, which verified the assumption of the influence of left PMd on right M1. These results suggested the common and separate character of underlying mechanisms of ME and MI, and indicated how the brain regions were inter-activated associated with handedness during both conditions.5. The dynamic causal model (DCM) established on the neuronal level was applied to fMRI data of ME and MI tasks related to dominant and nondominant hand of right-handed subjects, to detect the dynamic networks of the motor system during both conditions and the influence of the external experimental stimuli on the activated brain regions and the effective connectivities, as well as the difference between the two networks. The results showed a foreward and backward loop during left and right SMA, and the effective connectivity from contralateral SMA to contralateral M1 in each of the four diagrams. During MI, contralateral SMA corresponding to the performing hand exerted suppressive influence over the contralateral M1. In addition, the external stimuli were found to have the stimulative or suppressive influence over activated brain regions in both ME and MI networks. When comparing two dynamic networks during ME and MI, the transforming between the stimulative and suppressive role of the external stimuli on the certain activated areas was exhibited.
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