Abstracts

We recently reported cortical and thalamic fMRI BOLD responses in patients with idiopathic generalized epilepsy ([italic]Agha Khani et al. [/italic][italic]Brain:127;1127-1144[/italic]). In order to better understand the role of the thalamus in spike synchronization and propagation, we investigated patients with focal epilepsy and compared the BOLD responses in the thalamus and cortex in those with or without bilateral synchrony (BS). We used combined EEG-fMRI in 64 patients with focal epilepsy who had active interictal spiking during routine or telemetry recording. Twenty-one Ag/AgCl electrodes were applied using the 10-20 system (EMR32 amplifier, Schwarzer, sampling rate 1000Hz, EEG processed off-line to filter out the scanner artifact). MR images were obtained with a 1.5T scanner (Vision), and at the start of each study an anatomical MR was performed (T1, 256x256 sagittal, 160 slices, 1 mm thick, slice gap of 0.2 mm). fMRI images were motion corrected and smoothed using in-house software (25 BOLD EPI 64x64 axial slices, voxel size 5x5x5 mm, TE 50 ms, flip angle 90[deg]). Study duration varied between 90 to 120 min. We performed statistical processing of the images using the method of Worsley et al. in order to find the areas that changed in response to the epileptiform discharges. A response could either consist of an activation (positive BOLD) or of a deactivation (negative BOLD). Forty patients had spikes during fMRI scanning. Twenty-nine had uni- or bilateral independent temporal or extratemporal spikes without BS (group 1), and 11 showed BS (group 2). Forty fMRI spike analyses were performed in group 1 with significant BOLD responses in 18 (45%). In the second group, all the patients showed a significant BOLD response. A thalamic response was found in 55% of the patients with BS compared to 25% with focal discharges only. The cortical BOLD responses were also more widespread in patients exhibiting BS. Cortical activation was the dominant response and had a better correlation with spike distribution in patients without BS, while those with BS showed both widespread positive and negative BOLD responses. We demonstrated metabolic and hemodynamic evidence of thalamic involvement in patients with focal epilepsy. Activation and deactivation in the thalamus and the cortex were more frequently observed in patients with BS and the cortical fMRI responses were more widespread compared to patients with focal spikes only. These findings support the role of the thalamus in the synchronization and propagation of spikes between the two hemispheres. The similarities in hemodynamic response between patients with BS and those with generalized epilepsy suggest a common underlying synchronizing mechanism. (Supported by CIHR MOP 38079)