Impairments Of Thalamocortical Network And Default Mode Network In Drug-resistant Epilepsy:A Diffusion Tensor Imaging Study

Objective Epilepsy is one of the most common chronic brain dysfunction diseases.Approximately one-third of epilepsy cases are drug-resistant,among which generalizedonset seizures are very common causes of drug-resistant epilepsy(DRE).This study used diffusion tensor imaging(DTI)to investigate the damage to the fibrous pathways of bilateral thalamocortical network and default mode network(DMN)of DRE:(1)To explore the structural connection mode of bilateral thalamocortical network in DRE patients,and further explored the correlation between the disease duration and the damage of thalamocortical pathways.Explain the pathophysiology mechanism of thalamic network in generalized epilepsy from the perspective of brain structural network.(2)To explore the damage of the structural connection of the DMN in brains of patients with DRE,and discuss the clinical significance.Methods(1)DRE group was composed of 15 DRE patients from the department of epilepsy surgery of the Provincial Hospital of Anhui Medical University.All patients were identified as generalized onset by long-term video electroencephalography monitoring and clinical symptomatology of epileptic seizures.In the same period,fifteen healthy volunteers who matched gender and age were recruited to form a healthy control(HC)group.All participants underwent DTI scans.According to the Brodmann areas,the cortex is divided into five Regions of interest(ROI): motor cortex(MC),prefrontal cortex(PFC),parietal-occipital cortex(POC),somatosensory cortex(SC)and temporal cortex(TC).Thirty cases of diffusion kurtosis imaging(DKI)data with high b-value from healthy young adult database of the Human Connectome Project(HCP)were collected for thalamic segmentation using FMRIB Software Library(FSL).The thalamus was divided into five subregions based on the strongest connection between thalamus and cortical regions and the results were fused and registered to the DRE group and the HC group.Using probabilistic fiber tracking method on two groups in the thalamocortical fiber pathways.The fractional anisotropy(FA),mean diffusivity(MD),axial dispersion(AD)and radial diffusivity(RD)of the pathways which has the largest space overlap were calculated and compared between HC and DRE groups.The Pearson correlation coefficients between diffusion parameters and the courses of disease were calculated in the DRE group.(2)DRE group was composed of 15 DRE patients from the department of epilepsy surgery of the Provincial Hospital of Anhui Medical University.At the same time,fifteen healthy subjects with age and gender matching were recruited to form the HC group.All subjects collected DTI and T1 data.The fiber bundle paths of DMN were acquired using probabilistic fiber tracking.Then calculated diffusion parameters such as FA and RD to form a DMN structure network.Compare the DMN structural connection differences between DRE group and HC group.Results(1)Binarization pathways between different individuals in the group has the highest rate of space overlap under the 5% probabilistic threshold.Probabilistic tractography analyses showed that FA of thalamocortical pathways in DRE group decreased significantly(corrected P-value<0.001).RD of the left thalamus-MC pathway(corrected P-value=0.046)and left thalamus-POC pathway(corrected P-value=0.047)in the DRE group increased significantly.The AD and MD in all pathways had no significant difference(P-value>0.05).Pearson correlation results showed that in addition to the right thalamus-PFC pathway,FA of all other pathways(bilateral thalamus-POC,bilateral thalamus-MC,bilateral thalamus-SC,bilateral thalamus-TC and left thalamus-PFC)was inversely correlated with disease duration(corrected P-value<0.05).(2)Compared with the HC group,the cognitive ability of the DRE group decreased significantly,FA values of DMN structural connections generally decreased(P<0.05),and RD values increased(P<0.05).Abnormal structural connections involved all DMN brain regions.Conclusion(1)There are extensive fiber pathways between thalamus and cortex,these complex fiber bundles constitute thalamocortical network,which plays an important role in the generalized-onset epilepsy.In such patients,bilateral thalamocortical pathways are extensively impaired.This abnormal thalamic network may be the destruction of fiber bundles caused by epileptic seizures and may also provide the conditions for the widespread of epileptic discharge.Epileptic discharge can interfere with the differentiation of glial cells,destroy the myelin sheath,and affect the regeneration of myelin sheath,reduces the integrity of the nerve fibers eventually.The longer the disease duration,the more epileptic discharges,the degree of destruction of nerve fibers is more serious.Therefore,for patients with drug-resistant generalized epilepsy with longer disease duration,the treatment effect and prognosis may be worse.(2)The fiber pathway integration and connectivity of DMN in DRE patients are decreased,which may be an important reason for the abnormal DMN functional connection in DRE patients,and ultimately cause the ability obstacles in environmental monitoring,memory extraction,social cognition,self-control and other.