| Temporal lobe epilepsy(TLE)is the most common type of localization-related epilepsy associated with recurrent spontaneous seizures and cognitive dysfunctions.To date,these widespread deficits are still insufficiently understood.Recent studies promote the view that more complex contribution of thalamus for cognition.Thalamus do function not only as a passive relay station but also modulate information interaction involve in corticocortical processing.However,few studies have linked structural and functional disorders of thalamus with cognitive impairment in TLE patients.The application of high-resolution neuroimaging sequences and advanced modeling methods reveal the characteristics of brain activity,which have provided a deep insight into the cognitive mechanism of neurological diseases.Therefore,in this study,we aimed to demonstrate the thalamic structure and functional characteristics in patients with TLE based on multi-modality magnetic resonance imaging data,and their roles in cognitive performance.Part Ⅰ:Relationship between abnormalities in thalamic volume and structural covariance network and cognitive performance in patients with TLEObjective:The relationship between structural abnormalities in the thalamus and cognitive performance of TLE patients is still controversial.In this part,we aim to analyze the abnormalities in thalamic volume and its structural covariance network of TLE patients,and explore their relationship with cognitive performance.Methods:Fifty-three patients with TLE,including 22 patients with left TLE and 31 patients with right TLE,as well as 37 matched healthy controls were included in this study.All participants underwent structural and functional data acquisition on an MRI system scanner.The Montreal Cognitive Assessment(MoCA)was administered to assess their cognitive performance.Using voxel-based morphometry method,we conducted the group-wise comparisons in gray matter volume of thalamus.The seed-based structural covariance network analysis was performed to generate the structural network of thalamus.A correlation analysis was performed between the abnormal thalamic network and cognitive performance in TLE patients.Results:Compared with healthy controls,the abnormal gray matter volume of thalamus in left TLE or right TLE patients mainly located in the medial thalamic region.Also,patients with TLE showed decreased thalamic structural connectivity among extensive brain regions,such as insula,middle frontal gyrus,superior frontal gyrus,inferior temporal gyrus,anterior cingulate gyrus and so on.We did not find a correlation between the thalamic atrophy and cognitive performance.But the disrupted thalamic structural network showed significant correlated with cognitive dysfunctions.Conclusion:TLE patients exhibit thalamic atrophy,as well as thalamic structural network abnormality.The significant correlation between the cognitive decline in TLE patients and the disrupted structural covariance network of thalamus suggest that,the role of thalamus in cognitive impairment was mediated by structural covariance network.Part Ⅱ:Relationship between abnormalities in thalamic functional connectivity network and cognitive performance in patients with TLEObjective:As a heterogeneous subcortical structure,thalamus projects extensive interconnection to cerebral cortex.This anatomical basis highlights the role of the thalamus in cognitive dysfunctions of TLE patients.In this part,we aim to analyze the abnormality in functional connection network of thalamus in TLE patients,and explore their relationship with cognitive performance.Methods:Fifty-three patients with TLE,including 22 patients with left TLE and 31 patients with right TLE,as well as 37 matched healthy controls were included in this study.All participants underwent structural and functional data acquisition on an MRI system scanner.The MoCA was administered to assess their cognitive performance.The seed-based functional connectivity network analysis was performed to generate the functional network of thalamus.A correlation analysis was performed between the abnormal thalamic network and cognitive performance in TLE patients.Results:Compared with healthy controls,disrupted functional connectivity in TLE patients was observed between thalamus and vermis,right supplementary motor area,caudate.The increased thalamic functional connectivity was mainly observed in left supplementary motor area,cingulum,postcentral gyrus,middle occipital gyrus,right middle frontal gyrus and bilateral superior temporal gyrus.The abnormal thalamic functional network showed significant correlated with cognitive dysfunctions.Conclusion:TLE patients exhibit thalamic functional network abnormality.The cognitive decline in TLE patients show significant correlation with the disrupted thalamic functional connection network.Further research is needed from the thalamocortical network perspective to explore the cognitive role of the thalamus in TLE patients.Part Ⅲ:Module structure analysis of thalamocortical network in TLE patients and the influence on cognitive performanceObjective:The thalamus participates in multiple cognitive functions and maintain the modular structure of cortical functional networks.The disrupted modular organization of thalamocortical functional networks may explain the cognitive impairment in TLE patients.In this part,we aim to analyze the abnormality in module structure of thalamocortical network in TLE patients,and explore their influence on cognitive performance.Methods:Fifty-three patients with TLE,including 22 patients with left TLE and 31 patients with right TLE,as well as 37 matched healthy controls were included in this study.All participants underwent structural and functional data acquisition on an MRI system scanner.The MoCA was administered to assess their cognitive performance.Using graph-theory approach,we calculated the global modularity,within-module connectivity,between-module connectivity and modular segregation index.For each thalamic subdivision connected with different functional network,the participation coefficient and the within-module degree were calculated.A correlation analysis was performed between the abnormal modularity features and cognitive performance in TLE patients.Results:Compared with healthy controls,the global modularity and modular segregation index of ventral attention network and default mode network in right TLE patients showed significantly decreased.The connectivity between somatomotor network and ventral attention network and their connected thalamic subdivision showed significantly decreased in patients with right TLE.The participation coefficient of thalamic subdivision connected with somatomotor network presented increased in both left and right side TLE patients.The withinmodule degree of thalamic subdivision connected with somatomotor network presented increased in right side TLE patients,while the thalamic subdivision connected with default mode network presented decreased in left side TLE patients.The altered modular characteristics were associated with a worsening cognitive performance of TLE patients.Conclusion:The abnormalities in the modular characteristics of network highlight the abnormal separation and integration of brain network in TLE patients.The thalamus act as a critical hub in the brain network that could relay and integrate different information and maintain the modular structure of functional network.These abnormal modular characteristics have negative effects on cognitive behavior,which may present the neural mechanism of cognitive impairment in TLE patients.Part Ⅳ:Dynamic functional connectivity analysis of thalamocortical network in TLE patients and the influence on cognitive performanceObjective:The abundant information contained within the dynamic characteristics of functional connectivity might provide a more comprehensive understanding in human brain networks.In this part,we focus on the variability in the thalamocortical connections,as well as temporal features of the connectivity state and variability of global organization in patients with TLE.We aim to extend the understanding of the pathophysiological network mechanisms involved in cognitive impairment.Methods:Fifty-three patients with TLE,including 22 patients with left TLE and 31 patients with right TLE,as well as 37 matched healthy controls were included in this study.All participants underwent structural and functional data acquisition on an MRI system scanner.The MoCA was administered to assess their cognitive performance.The spatial independent component analysis and sliding-window approach were applied to obtain dynamic functional connectivity patterns.kmeans clustering was performed to classify the recurring connectivity states.Then the temporal properties of the functional connectivity states were explored.The variability of the network topological organization and functional connectivity was calculated to assess fluctuations of functional connectivity across the sliding windows.Correlation analyses were conducted between abnormal dynamic properties and cognitive performances.Results:Compared with healthy controls,the dynamic functional connectivity between thalamus and inferior parietal lobule showed increased variability in TLE patients.The clustering results presented two discrete connectivity states at the whole-brain level.The reoccurrence fraction and dwell time for state Ⅰ(the withinnetwork connected pattern)in TLE patients was shortened,while state Ⅱ(the between-network connected pattern)increased.Also,TLE patients showed increased variability in network properties,i.e.,normalized characteristic path length(λ),global network efficiency(Eglob)and local network efficiency(Eloc).The altered dynamic characteristics were associated with a worsening cognitive performance of TLE patients.Conclusion:The variability of thalamocortical connection might represent a mechanism for dynamic reconfiguration of brain networks.The abnormalities in the dynamic functional connectivity highlight the vulnerability of brain networks,and the variability analysis based on graph-theory support the abnormal separation and integration of brain network in TLE patients.These abnormal dynamic network characteristics have negative effects on cognitive behavior,which may present the neural mechanism of cognitive impairment in TLE patients. |
PDF Full Text Request