Abstracts

Periventricular nodular heterotopia (PNH) is a malformation of cortical development characterized by abnormal migration of neurons, which remain grouped in nodules around the ventricles. Scalp EEG findings in PNH patients are frequently related to the location of the nodules, which often show epileptogenicity, as demonstrated by recordings with depth electrodes. We investigated whether interictal scalp EEG abnormalities are associated with functional magnetic resonance imaging (fMRI) responses in the nodules or close cortical regions, using continuous EEG-fMRI. Seven PNH patients underwent two-hours continuous EEG-fMRI monitoring with 21 MRI compatible scalp electrodes and amplifier. BOLD-EPI fMRI data were collected in runs of six minutes with the patient in the resting state. EEGs were filtered offline and spikes were marked according to spatial distribution and morphology. Maps of the t statistic (t-maps) were created using the timing of the spikes as events for fMRI analysis. At each voxel, the maximum t value was taken from t-maps created using four haemodynamic response functions with peaks at 3, 5, 7 and 9 seconds. BOLD-fMRI responses were defined as positive (activation) and negative (deactivation) for voxels which exceeded a corrected p=0.01. We determined if the maximum t-value for activation and deactivation occurred in the nodules or in the cortical area corresponding to the region of the nodules. All patients showed spikes during EEG-fMRI, but one patient had only one spike, and was not analysed further. One patient had four types of spikes and therefore a total of nine studies were analysed. In 7/9 studies, the spike spatial distribution on the scalp was concordant with nodule location. Four studies showed fMRI activations and deactivations, one only activation and three only deactivations. Activation was found in 5/9 (55%) studies, and did not involve the nodules. Maximum activation was in the cortical area corresponding to the nodule in two patients and in a remote area in the other three. Deactivation was found in 7/9 (78%) studies and was also always outside the nodules. Maximum deactivation was in the cortical area corresponding to the nodule in three patients, in a remote cortical area in three studies and in the thalamus in one study. EEG-fMRI responses in PNH patients were predominantly negative and not in the nodules. This may be due to the fact that we did not acquire fMRI data related to EEG abnormalities from inside the nodules. (Supported by grant MOP 38079 of the Canadian Institutes of Health Research. EK receives a Preston Robb fellowship from the Montreal Neurological Institute.)