Large-scale cortico-subcortical functional networks in focal epilepsies: The role of the basal ganglia

Abstract

ObjectivesThe aim was to describe the contribution of basal ganglia (BG) thalamo-cortical circuitry to the whole-brain functional connectivity in focal epilepsies.MethodsInterictal resting-state fMRI recordings were acquired in 46 persons with focal epilepsies. Of these 46, 22 had temporal lobe epilepsy: 9 left temporal (LTLE), 13 right temporal (RTLE); 15 had frontal lobe epilepsy (FLE); and 9 had parietal/occipital lobe epilepsy (POLE). There were 20 healthy controls. The complete weighted network was analyzed based on correlation matrices of 90 and 194 regions. The network topology was quantified on a global and regional level by measures based on graph theory, and connection-level changes were analyzed by the partial least square method.ResultsIn all patient groups except RTLE, the shift of the functional network topology away from random was observed (normalized clustering coefficient and characteristic path length were higher in patient groups than in controls). Links contributing to this change were found in the cortico-subcortical connections. Weak connections (low correlations) consistently contributed to this modification of the network. The importance of regions changed: decreases in the subcortical areas and both decreases and increases in the cortical areas were observed in node strength, clustering coefficient and eigenvector centrality in patient groups when compared to controls. Node strength decreases of the basal ganglia, i.e. the putamen, caudate, and pallidum, were displayed in LTLE, FLE, and POLE. The connectivity within the basal ganglia–thalamus circuitry was not disturbed; the disturbance concerned the connectivity between the circuitry and the cortex.SignificanceFocal epilepsies affect large-scale brain networks beyond the epileptogenic zones. Cortico-subcortical functional connectivity disturbance was displayed in LTLE, FLE, and POLE. Significant changes in the resting-state functional connectivity between cortical and subcortical structures suggest an important role of the BG and thalamus in focal epilepsies.

Deep brain activities can be detected with magnetoencephalography

“…Our results suggested the detectability of such deep brain regions on MEG as previously modeled 9,47 and reported 48,49 . It has long been argued that focal epilepsy is a cortico-subcortical disease 50,51 and the role of thalamus in epilepsy has gained renewed interest 52–55 . Taken together, these data offer the opportunity in the future to non-invasively study the actual extension of the limbic epileptic network to such brain structures believed to be undetectable on surface.…”

Brain Functional Connectivity Changes After Transcranial Direct Current Stimulation in Epileptic Patients

“…FC alterations play a crucial role in focal epilepsy. Actually, recent neuroimaging studies confirmed that focal epileptic neurons create an own pathologic network and its activity can interfere with other cortico-subcortical networks causing a broad spectrum of cognitive disabilities ( Rektor et al, 2013 ; Moshé et al, 2015 ; Englot et al, 2016 ; Výtvarová et al, 2017 ). Furthermore, epileptic activity drives a certain degree of plastic reorganization of brain networks ( Englot et al, 2015 ; Gleichgerrcht et al, 2015 ).…”

Longitudinal MRI Evaluation of Ischemic Stroke in the Basal Ganglia of a Rhesus Macaque (Macaca mulatta) with Seizures

“…22 In addition, a recent MRI study of patients revealed significant changes in the resting-state functional connectivity between cortical and subcortical structures, indicating the important role of the basal ganglia and thalamus in focal epilepsies. 48 In comparison to the other macaques with permanent MCA occlusion in the same cohort, our macaque with seizures lacked prominent ischemic infarction in the cortex, due to the abundant collateral blood supply in NHP. 45 Instead, ischemic infarction was confined to the caudate on the day of surgery and extended to the putamen at 48 h after stroke.…”