Abstracts

Rationale: Previous studies support the role of thalamocortical network in the basic pathogenesis underlying primarily generalized epilepsies and secondary generalization from mesial temporal lobe. However, the structural and functional characteristics of the network in focal neocortical seizures have not yet been determined. Methods: We recruited 16 patients with focal seizures showed that a history of secondarily generalized seizures, normal MRI and medical effectiveness. These patients did not have typical auras, seizure presentations, imaging findings or EEG discharging for diagnosing mesial temporal lobe epilepsy. We used high-resolution T1-weighted, diffusion-tensor and resting-state functional (RS-f) MR images to study the thalamocortical connections. We used voxel-based morphometry to compare the thalamic and cortical gray matter (GM) density, and the white matter (WM) fractional anisotropy (FA) between the patients and 16 age-matched normal controls. And we connected whole thalamus as a seed and 7 sub-thalamic seeds to measure the functional connectivity (FC) of thalamocortical network with cortices. Results: In the patients, there were significant GM density decreases in the thalamus, left postcentral gyrus, left superior frontal gyrus and left supplementary motor area. The peak coordinate location of the reduced thalamus density cluster was over the mediodorsal region. The patients had decreased FA values in the left external capsule and bilateral anterior corona radiatae. When seeding whole thalamus to evaluate the thalamocortical FC with cortices, right inferior frontal gyrus, right superior frontal gyrus, left inferior temporal gyrus and left middle frontal gyrus demonstrated high association with the thalamus. Through a 7-sub-thalamic seeds atlas that thalamic parcellation was based on WM connectivity to cortices, more cortices were identified to have FC differences with different sub-thalamic regions. The right inferior frontal and superior frontal gyri were consistently presented with high connectivity to a prefrontal association sub-thalamic seed. Anatomically, the sub-thalamic region contains mediodorsal neucleus. Conclusions: Although our patients have no visible MRI lesion and rare generalized convulsions, their thalamic GM and thalamus-associated WM still have microstructural changes. The functional connections between the thalamus and cortices of patients are different from normal subjects. Especially, the functional and structural changes of mediodorsal thalamic nucleus are consistent with the study results of primarily generalized epilepsies and mesial temporal lobe epilepsy. Funding: This work was supported in part by the Ministry of Science and Technology, Taiwan, under the project MOST 103-2220-E-040-001 and in part by the "Aim for the Top University Plan" of National Chiao Tung University and the Ministry of Education, Taiwan.