Abstracts

Rationale: Focal epilepsy is a neurological disorder affecting neural networks beyond the seizure focus. However, underlying network alterations in focal epilepsy are still poorly understood. In this study, we used a novel functional MRI approach called Dynamic Regional Phase Synchrony (DRePS), to detect brain areas with abnormal regional dynamic connectivity (at TR-resolution) in people with extratemporal focal epilepsy.Methods: Patients with extratemporal focal epilepsy were recruited from the Austin Hospital pre-surgical Epilepsy Program. In total, 19 patients with extratemporal focal epilepsy (mean age: 30.1.4 ± 11.5 s.d, 9 female) and 19 healthy controls (mean age: 30.9 ± 9.5 s.d, 12 female) were included. Ten minutes of task-free fMRI were acquired at 3T with a TR of 3000ms. The data was slice-timed, realigned (24 motion parameters) and co-registered to T1 images, segmented and normalised into MNI space (3x3x3 mm voxels). The data was band-pass filtered (0.03-0.07 Hz) while CSF and white matter signals were regressed out. Any data points with high head-movement (framewise displacement > 0.5mm), was removed and interpolated using a cubic spline algorithm. For analysis, DRePS was calculated by estimating voxel-wise regional connectivity (connectivity between a centre voxel and its 26 immediate neighbours) using instantaneous phase information between successive time-points, allowing for single time-point (TR) analysis. To quantify the frequency content of DRePS, the sum of the power spectral density from the obtained 4D DRePS time-series were calculated (see figure 1B-C). Non-parametric permutation testing was used to estimate between group differences (200000 permutation) with a statistical significance level at p < 0.001 (FDR-corrected).Results: Higher DRePS frequency (sum power-spectral density) was seen in focal epilepsy subjects in the right inferior frontal gyrus and right anterior insula/claustrum (p < 0.001, FDR corrected). In focal epilepsy, decreased DRePS frequency (sum power-spectral density) was observed in the precuneus (p < 0.001, FDR corrected). See figure 2 for results.Conclusions: In focal epilepsy, altered regional dynamic connectivity was observed in brain regions comprising the right fronto-insular cortex and the precuneus - these are brain areas critical for response inhibition (right inferior frontal gyrus), salience/task-swiching (right anterior insula) and ‘resting-state’ network activity (medial precuneus). These brain areas may be a part of faulty large-scale network behaviour that is important to focal epilepsy.