Community-informed connectomics of the thalamocortical system in generalized epilepsy

OBJECTIVE. We studied the intrinsic organization of the thalamo-cortical circuitry in patients with generalized epilepsy with tonic-clonic seizures (GTCS) via resting-state fMRI (rs-fMRI) connectome analysis and evaluated its relation to drug-response.

METHODS. In a prospectively-followed sample of 41 patients and 27 healthy controls, we obtained rs-fMRI and structural MRI. After one year of follow-up, 27 patients were classified as seizure-free and 14 drug-resistant. We examined connectivity within and between resting-state communities in cortical and thalamic subregions. In addition to comparing patients to controls, we examined associations to seizure control. We assessed reproducibility in an independent cohort of 21 patients.

RESULTS. Compared to controls, patients showed a more constrained network embedding of the thalamus, while frontocentral neocortical regions expressed increased functional diversity. Findings remained significant after regressing out thalamic volume and cortical thickness, suggesting independence from structural alterations. We observed more marked network imbalances in drug-resistant compared to seizure-free patients. Findings were similar in the reproducibility dataset.

CONCLUSIONS. Our findings suggest a pathoconnectomic mechanism of generalized epilepsy with generalized tonic and clonic seizures, centered on diverging changes in cortical and thalamic connectivity. More restricted thalamic connectivity could reflect the tendency to engage in recursive thalamo-cortical loops, which may contribute to hyper-excitability. Conversely, increased connectional diversity of frontocentral networks may relay abnormal activity to an extended bilateral territory. Network imbalances were observed shortly after diagnosis and related to future drug-response, suggesting clinical utility.