Structural–functional coupling changes in temporal lobe epilepsy

Abstract

Alterations in both structural connectivity (SC) and functional connectivity (FC) have been reported in temporal lobe epilepsy (TLE). However, the relationship between FC and SC remains less understood. This study used functional connectivity MRI and diffusion tensor imaging to examine coupling of FC and SC within the limbic network of TLE, as well as its relation to epilepsy duration, regional changes, and disease laterality in 14 patients with left TLE, 10 with right TLE, and 11 healthy controls. Structural and functional networks were separately constructed and the correlation estimated between structural and functional connectivity. This measure of SC–FC coupling was compared between left/right TLE and controls, and correlated with epilepsy duration. Elastic net regression was used to investigate regional structural and functional changes associated with SC–FC coupling. SC–FC coupling was decreased in left TLE compared to controls, and accompanied by reductions in FC for left and right TLE and in SC for left TLE. When examined in relation to disease duration, an increase in SC–FC coupling with longer epilepsy duration was observed, associated predominantly with structural loss of the fusiform and frontal inferior orbital gyrus in left TLE and functional hub redistribution in right TLE. These results suggest that decoupling between structural and functional networks in TLE is modulated by several factors, including epilepsy duration and regional changes in the fusiform, frontal inferior orbital gyrus, posterior cingulate, and hippocampus. SC–FC coupling may provide a more sensitive biomarker of disease burden in TLE than biomarkers based on single imaging modalities.

Regional and global connectivity disturbances in focal epilepsy, related neurocognitive sequelae, and potential mechanistic underpinnings

“…Furthermore, using graph theory analysis, Haneef et al noted global decreases in resting fMRI connectivity in MTLE, along with a progressive reduction in connectivity diversity over time. Several other investigations have also demonstrated positive relationships between disease severity and/or duration with intrinsic connectivity aberrations in various networks of both MTLE and FNE patients. Although directionality cannot be definitively established from these correlational studies, the progressive nature of connectivity alterations seen in focal epilepsy suggests that brain network perturbations likely develop over time with recurrent seizures, and are less likely to represent inherent network properties that predispose the brain to developing epilepsy.…”

WONOEP appraisal: Network concept from an imaging perspective

“…Regularization of whole‐brain network topology as well as pronounced shifts in the distribution of hubs and modularity were collectively reported across modalities, including structural MRI, diffusion MRI, and electroencephalography (EEG)–derived networks . Graph‐theoretical studies also indicated reduced coupling between structural and functional networks, which may be partially modulated by disease duration …”

“…69 Graph-theoretical studies also indicated reduced coupling between structural and functional networks, which may be partially modulated by disease duration. 70 With respect to functional connectivity measures, restingstate fMRI (rs-fMRI) studies found impaired connectivity of mesiotemporal structures, mostly involving links between anterior and posterior hippocampus, and between anterior hippocampus and entorhinal cortex, ipsilaterally. 71 Reduced functional connectivity was additionally detected between ipsi-and contralateral hippocampus, insula, and between ipsilateral mesiotemporal structures and bilateral lateral temporal neocortices.…”

Development of large-scale functional networks from birth to adulthood: A guide to the neuroimaging literature

“…Given that macroscale FC is modulated by both interregional connectivity strength as well as local population dynamics (Sanz-Leon et al, 2015), alterations in SC-FC coupling could potentially point to important shifts in the underlying drivers of various network phenomena. At least two reports have found abnormally low SC-FC correlation in epileptic patients (Chiang et al, 2015; Zhang et al, 2011), highlighting that aberrant SC-FC coupling may indeed indicate aberrations in neuronal physiology.…”