The Application Of Navigated Transcranial Magnetic Stimulation In Language Mapping

Background: Gliomas are the most common primary tumor in the central nervous system(CNS).The treatment of gliomas include surgical resection,radiotherapy,chemotherapy,targeted therapy and so on.Foremost among these treatment is surgical resection.At present,the basic principle of gliomas surgery is “maximum safe resection”.“Maximum resection” can fairly achieved through using intraoperative magnetic resonance imaging,neuronavigation system,microsurgical technique.However,“safe resection” is constrained by the current function mapping techniques.Individualized function mapping still need to improve.Navigated transcranial magnetic stimulation can generate a magnetic field which will penetrate the skull and induce a current to stimulate the brain both non-invasively and accurately.It has a promising application in preoperative language mapping.The aim of this study is to establish a Chinese language mapping method based on navigated transcranial stimulation and to investigate the distribution pattern of essential language sites.Furthermore,by combining diffusion tensor tractography(DTT),this study investigates the hodotopical organization of language function and provides reliable information of language function which will assist to accomplish the “safe resection” principle in surgical treatment of gliomas.Methods: This study includes two sections.First section is to establish a Chinese language mapping method based on navigated transcranial magnetic stimulation(n TMS).First,ideal language mapping protocol for Chinese was investigated by repeated language mapping of each subject using different protocols which had differences in stimulus frequency and intensity.Second,a panel of tasks,included counting,Chinese reading,picture naming and semantic judgement task,were used to investigate the most ideal task in Chinese language mapping.Finally,with ideal stimulation protocol and task,the distribution pattern of essential language sites in a group of healthy Mandarin-speaking people were investigated.Second section is to investigate the cortical termination of language relevant fibers and their relationship with essential language sites.First,language relevant fiber tracts were reconstructed from DTI data volume using a series of neuroimaging tool.The cortical terminations of each fiber tract were described in a cortical parcellation system.Second,by combining the location of essential language sites and language relevant fiber tracts,the hodotopical organization were investigated and described in posterior inferior frontal gyrus.Finally,through analyzing the relationship between arcuate fasciculus and essential language sites,the probability of using the termination of arcuate fasciculus as the indicator of essential language sites were studied.Results: In the first section:(1)Speech error rate induced by n TMS was increased accompany with the increasing of stimulus intensity and frenquency.By analyzing the error rate,VAS score and the distribution pattern of error sites,this study recommend “110% RMT,5Hz-10 pulses”as ideal protocol in Chinese language mapping.A fine adjustment based on the ideal protocol was needed due to individual differences.(2)Different language tasks evoked different language error rates and distribution pattern.Among all tasks,picture naming task presented the highest error rate and widest distribution range.Therefore,we considered picture naming task was the most ideal task in Chinese language mapping.(3)By using the ideal protocol and task,the present study unvealed the distribution pattern of essential language sites among healthy Mandarin-speaking people.Essential language sites had a disperse distribution pattern in per-subject level.However,some brain regions presented aggregration of essential language sites in group level,for example,ventral precentral gyrus in frontal lobe,middle and posterior superior temporal gyrus in temporal lobe and supramarginal gyrus in inferior parietal lobe.In the second section:(1)The reconstruction of language relevant fiber tracts revealed a cortical projection pattern of each fiber tract.(2)Essential language sites located in different area within posterior inferior frontal gyrus were conducted through different language relevant fiber tract.In ventral precentral gyrus,the essential language sites were predominately conducted through long segment of arcuate fasciculus(AF)and anterior segment of AF.In pars opercularis,the essential language sites were predominately conducted through aslant fiber tract.In pars triangularis,the essential language sites were predominately conducted through inferior frontal occipital gyrus.(3)AF can act as an indicator of essential language cortices only in a few regions among all brain regions.Therefore,the present results indicated a high risk of misidentifying the essential language sites when using AF termination as an indicator of essential language areas in whole brain regions around the perisylvian except ventral precentral gyrus.Conclusions:(1)n TMS is capable of mapping Chinese language function.Essential language sites presented a disperse distribution pattern in individual level and an aggregation trends in some particular brain regions in group level.(2)Language function follows the hodotopical organization.Essential language sites within distinct areas were conducted through different fasciculus.The termination of AF can act as the indicator of essential language sites practically only in ventral precentral gyrus.