Abstracts

Rationale: Spike-triggered EEG-fMRI studies show that epileptic activity may affect brain areas well beyond the epileptogenic cortex, including areas that are engaged in the "default mode network" (DMN) (Gotman, Epilepsia, 2008). A functional brain connectivity study using functional magnetic resonance imaging (fMRI) was performed to find DMN differences between patients with epilepsy and healthy volunteers. Methods: Ten healthy volunteers and twenty-four epileptic patients (14 with extra-temporal and 10 with temporal epilepsy) participated in the study. Resting state fMRI data, acquired with no explicit task, were obtained using the 1.5 T Siemens Magnetom Symphony scanner. Three hundred scans were obtained from the healthy volunteers, and two runs of 300 or 400 scans were obtained from the epileptic patients. For each subject, an independent component analysis (ICA) was used to separate the BOLD signal into spatially independent components, using the Group ICA of fMRI Toolbox (GIFT) program. In the ICA approach, one or several independent components could be related to epileptic activity anywhere in the brain, independent of the occurrence of spikes on the scalp. The component representing the DMN was chosen according to a spatial correlation with a mask typical for DMN (included in the GIFT program). A second-level analysis was calculated to evaluate differences among the DMN components in the healthy volunteers, patients with temporal epilepsy, and patients with extra-temporal epilepsy using SPM software. Results: In healthy subjects, the basal ganglia were functionally negatively correlated with typical DMN regions, such as the posterior medial and prefrontal cortices. This negative correlation was significantly lower in the two groups of patients with temporal and extra-temporal epilepsy. Conclusions: Unlike in healthy subjects, in epileptic patients the basal ganglia are not correlated with a DMN component. This may be interpreted as a sign of an altered or modified function of the basal ganglia in epilepsy.