Abstracts

Rationale: Several studies have sought to understand whether patients with frontal lobe epilepsy (FLE) demonstrate macro- and/or microscopic changes in their brain networks. The majority of studies have focused on functional connectivity, most commonly by means of resting state fMRI. A smaller number of studies have focused on structural connectivity, that is, the physical white matter pathways that link different regions of the brain, although these were conducted mostly among pediatric populations, or concentrated on specific sub-regions (e.g. supplementary motor area), or analyzed specific DTI features (e.g. functional anisotropy). The goal of this pilot study was, rather, to compare the structural connectome of adult patients with FLE and healthy controls using a “whole brain” approach. By doing so, we sought to identify potentially anomalous white matter tracts among patients with FLE in terms of fiber density (i.e., significantly stronger or weaker than paired controls) without a priori anatomical assumptions. Methods: Eight adult patients with diagnosis of FLE (50% male, aged 35.1 ± 12.0) and twenty age- (t26 = 0.86, p = .40) and gender- (χ2= 0.54, p = .46) matched controls (35% male, aged 31.1 ± 10.8) underwent MRI diffusion tensor imaging. Their structural connectomes were constructed using probabilistic tractography based on a cortical atlas (AICHA) of 384 distinct regions of interest (ROI). We then conducted whole brain link-by-link t-test comparisons between patients and controls. Results: Of all possible 147,072 connections, four were significantly different (p < .001) between patients and controls. Of these, two connections involved a ROI in the frontal lobes: the link between the right superior frontal gyrus and the right caudate was significantly stronger among controls (t = 4.29, p = .0002), and the link between   the right anterior rostral region and the left parieto-occipital area was significantly stronger among patients (t = -4.05, p = .0004). The other two significantly different connections were extra-frontal and both were stronger among patients with FLE: the link between the right lingual gyrus and the right superior temporal region (t = -4.49, p = .0001), and the ink between the left hippocampal and parahippocampal areas (t = -4.15, p = .0003).  Conclusions: This pilot study employed a whole brain comparison of the structural connectome between patients with FLE and healthy controls to identify abnormal brain links. We showed that a small number of connections involving both frontal and extra-frontal regions are abnormally strong or weaker among patients. The varied nature of these abnormal links likely reflects the heterogeneous small sample of patients analyzed here, but these results shed light on the potential clinical and theoretical utility of studying the structural connectome in epilepsy. Funding: No funding was received for this project.