Abstracts

Simultaneous EEG and functional MRI (fMRI) allow evaluation of BOLD responses related to interictal spikes. Our objective was to investigate the extension of EEG-fMRI responses related to spikes in TLE patients. We performed two-hour continuous EEG-fMRI recordings using 21 MRI compatible electrodes and amplifier. BOLD-EPI fMRI acquisition parameters were: 5x5x5 mm voxel, 25 slices, 64x64 matrix, TE = 50 ms, TR = 3 s, flip angle 90[deg]. EEGs were filtered to remove the scanning artefact and spikes were marked using FEMR or Vision Analyser softwares. Maps of the t statistic (t-maps) were created with the timing of spikes as events in the fMRI analysis. At each voxel, the maximum t value was taken from four t maps created with hemodynamic response functions peaking at 3, 5, 7 and 9 seconds. BOLD-fMRI responses were defined as positive (activation) and negative (deactivation), for voxels exceeding a corrected p=0.01. Localization of responses was determined by co-registration of anatomical and t-maps. We studied 28 patients with lesional and seven patients with non-lesional TLE. The lesional group included patients with hippocampal atrophy (n = 5), atrophy/gliosis of TL neocortex (n = 3), developmental mesial temporal abnormalities (n= 5), and other TL lesions (n= 9). Eight patients had no spikes during the scan, and eight others had independent bitemporal spikes, which were analysed separately, giving a total of 35 EEG-fMRI studies. Twelve studies showed only activation, 14 both activation and deactivation, and three only deactivation. Eighteen studies had TL activation: 12 were bitemporal, four ipsilateral to EEG spiking and two contralateral. Associated extra-temporal activation was seen in 16 of them. Eight studies showed only extra-temporal activation.
Eight studies showed TL deactivation: four bitemporal, two ipsilateral and two contralateral. Nine studies showed only extra-temporal deactivation, and all eight studies with TL deactivation also showed extra-temporal deactivation. TL responses were more frequently neocortical, with or without concomitant mesial involvement. Extra-temporal responses were either ipsilateral or bilateral. Basal ganglia and thalamic responses were seen in five studies, while cingulate responses were observed in nine studies. EEG-fMRI responses were observed in most TLE patients and were in general more widespread than expected, involving also the TL contralateral to the spikes, and some extra-temporal areas, including the thalamus. fMRI responses in the TLs were predominantly neocortical and bilateral, even in patients with unilateral spikes. These results point to a potential effect of epileptic spikes beyond their place of generation. (Supported by grant MOP 38079 of the Canadian Institutes of Health Research. EK receives a Preston Robb fellowship from the Montreal Neurological Institute.)