The Application Of Navigated Transcranial Magnetic Stimulation In Motor Cortex Mapping

Backgroud: Mapping eloquent area of the brain is the crucial procedure in neurosurgical clinical works,because the localization of functional cortices not only related to the choice of the surgical approach,but also determines the extent of surgical resection,and may also affects the postoperative recovery and prognosis.Therefore,by combining with microsurgery neuroendoscopy and neuronavigation technology,the current neurosurgical concepts has broken the previous restricted area,and promote the surgical philosophy of “maximizing the extent of tumor removal while maximizing the preservation of neurological function”.In the non-eloquent areas,the lesions can be completely resected or even expandingly resected,but if the lesions located in the eloquent areas,the benefits and risks of operation should be evaluated prudently.In terms of central nervous system tumors,surgical resection of tumor is the beginning of comprehensive treatments which directly affect the prognosis of patients.Navigated transcranial magnetic stimulation(n TMS),a new method of noninvasive brain stimulation,which can generate time-varying magnetic field penetrating the skull noninvasively and stimulate cerebral cortex accurately by induced current,shows its value in neuroscience.In this study,we established the motor cortex area localization method and evaluated the feasibility and accuracy of the method based on transcranial magnetic stimulation hardware and software system.Then we established and verified the data analysis method of evaluating the reorganization and plasticity pattern of motor cortex area in order to provide a feasible method to localize motor cortex area preoperatively and then evaluated motor function postoperatively in brain tumor treatment.Finally,we tried to make it possible to apply the n TMS technique to complete preoperative planning,intraoperative mapping and postoperative evaluation in neurosurgical brain tumor management.Methods: This study included three sections.In the first section,we tried to establish the method of motor cortex mapping based on n TMS hardware and software system.We investigted and analyzed the following parameters of motor cortex mapping such as resting motor threshold,stimulating coil direction,stimulating intensity,data error judgment,data extraction method and stimulating matrix arrangement method.Then we established the basic method and operating process of motor cortex localization,concluded data extraction and analysis methods in this study.In the second section,we localized hand motor cortex by n TMS using the method established in previous section and analyzed the test-retest reliability and stability.By using the unique method and formula we established,we tried to determine the localization results’ reliability and/or reorganization level in our study.And then we evaluated the accuracy and feasibility of the proposed method and formula by comparing with the experimental results computed by commonly used statistical method.In the third section,healthy subjects were recruited to carry out short-term exercise-induced function training.We judged the training results through behavioral index and functional magnetic resonance imaging analysis.By using the n TMS experimental methods established in previous sections,we localized the motor cortex area and analyzed the outcomes of exercise training,verified and evaluated the feasibility of the method,and further discussed the mechanisms of motor cortex area reorganization and plasticity pattern.Finally we analyzed the safety of TMS application retrospectively in this study.Results: The first section: TMS motor cortex mapping process had to be navigated in order to minimize the localization error,the preset grid matrix point spacing was 5mm,the stimulation direction must be perpendicular to the cortex surface and the orientation of the stimulating coil was 45° angle with the horizontal plane pointing to the top,the stimulating intensity was 110% of the resting motor threshold intensity.The Grubbs criterion was used to remove the coarse error.The extracted distance data was calculated according to the preset two-dimensional coordinate data.We chose the midpoints of the positive point and its adjacent negative point as motor cortex area boundary points,the extent of midpoint connection is the positive motor cortex area.The second section: Mapping processes were completed successfully in all volunteers,size of motor area resting motor threshold and max activation intensity showed preferably stability.Key points such as center,hotspot,center of gravity,max activation point and their vectors showed better stability.But the outcome stability of extent of positive motor distribution areas need further study.The localization results’ reliability of the method established in this study has a good correlation with the intraclass correlation coefficient statistical method,and could quantify parameters of motor cortex mapping.The third section: The f MRI results showed the exercise function induction training experiment can induce the reorganization and plasticity of the motor cortex area at a certain level.By using the method we established,we quantified the motor cortex area reorganization and plasticity level and its orientation,which showed good agreement with the results of f MRI.This method might further promote the application of preoperative and postoperative motor cortex mapping in brain tumor surgery management.In this study,all subjects had no adverse reactions,the overall experimental process were safe and controllable.Conclusion:(1)The n TMS method is capable of mapping motor cortex area,it can mapping accurately in individual level and keep stable repeatability in group level.(2)The localization results’ reliability of the method established in this study has a good correlation with the classical statistical method,and can quantify the repeatability and reorganization orientation level of motor cortex area.(3)The exercise function induction training experiment can induce the reorganization and plasticity of the motor cortex area at a certain level,the results of n TMS localization shows good agreement with the results of f MRI,but the stability of the reorganization of the motor cortex area need long-term study to determine.