Abstracts

Rationale: Functional connectivity of the default mode network (DMN), the main resting-state network of the brain, has been shown to be altered in patients with epilepsy compared with healthy controls. The posterior cingulate cortex (PCC)/precuneus is the main node of the DMN. Its functional connectivity has yielded conflicting results in previous studies of temporal lobe epilepsy (TLE). The other main nodes are the right and left lateral parietal cortices (LPC) and the mesial prefrontal cortex (MPFC). This study compared the functional connectivity of the PCC/Precuneus between patients with TLE and healthy controls. Methods: Twelve right-handed healthy volunteers (6 females, 6 males; median age 36.5 years, range 23-68) and 14 right-handed patients with non-lesional TLE (9 females, 5 males; median age 41.5, range 19-72) underwent 7-Tesla MRI scans. All TLE patients underwent prolonged video-EEG monitoring for seizure focus localisation (8 left TLE, 3 right TLE, 3 bilateral TLE). Except for two patients with left TLE, all other patients were deemed drug-resistant. All functional scans were preceded by high-resolution anatomical scans for localisation and co-registration purposes. Functional connectivity was calculated between the PCC/precuneus and the MPFC and bilateral LPC nodes via the CONN toolbox. Regions of interest were based on independent component analysis of the resting-state data of 497 healthy participants in the Human Connectome Project. Correlation coefficients were converted to normally distributed Z scores using Fisher’s transformation, and a mean Z score value was calculated for each participant. Results: Mean functional connectivity between the PCC/precuneus and the MPFC and bilateral LPC nodes was higher in the patients with TLE compared to the control group (0.956 vs. 0.733, p=0.0206 [Mann-Whitney U Test, figure 1]). The mean functional connectivity increased with age in both groups (figure 2), correlating significantly with age in the healthy controls (r=0.686, p=0.014) but not in the TLE patients (r=0.327, p=0.254). Conclusions: Resting-state functional connectivity within the DMN is higher in patients with TLE than in healthy controls. This could potentially relate to increased brain network excitability, and its connection to neurocognitive changes commonly seen in these patients should be further explored. Funding: The Royal Melbourne Hospital Neuroscience Foundation. The 7T MRI scanner and A/Prof BA Moffat are supported by the National Imaging Facility via the Australian Government NCRIS program. Dr.OM Gonen is supported by the Melbourne Research Scholarship.