Abstracts

Rationale: Recent dense array (256-channel) EEG studies of generalized spike-wave seizures in absence epilepsy (Holmes, et al., 2004) have suggested that the cortical control over the cortico-thalamo-cortical dysregulation in these seizures may involve midline frontal cortex specifically. Possibly consistent with these observations, dense array (256-channel) EEG studies of normal sleep have shown that the SCOs of sleep also arise most frequently in orbital and frontopolar regions (Massimini, et al., 2004). During long-term monitoring of epileptic patients with dense array EEG to determine seizure onset, we observed a generalized spike-wave seizure in one of the initial patients that appeared to evolve from the slow cortical oscillations of sleep. Methods: Both the SCOs and seizure discharges were source-analyzed with a linear inverse method (Michel et al, 2004) in the GeoSource software (Electrical Geodesics, Inc.). Results: In the seizure shown here, analysis of the final (apparently normal) SCO before seizure onset (time 1 in Figure 1) with average-reference topographic mapping (Figure 1) showed a left-lateralized distribution of the surface-negative potential over frontal regions. Source modeling of this potential distribution (time 1) shows the strongest distribution in left orbital and frontopolar regions. After a series of apparently normal SCOs, there was a small SCO (time 2 in Figure 1), then the apparent onset of the seizure with a widespread paroxysmal discharge. Figure 2 shows this small SCO at time 2 in topographic waveform view. Although it is more irregular than previous SCOs, this slow wave shows the same left frontal distribution as previous SCOs, and it showed the same left orbital maximum (with secondary activations in BA10 and left temporal pole) as previous SCOs. The initial, broadly-distributed paroxysmal discharge appears to evolve from this final small SCO, with a negative-positive spike over the left frontal region (Fp1, F3, F7), followed by an extended (1.5 sec) negative-going slow wave in these same channels, and finally the 3 per sec oscillations of the seizure. Conclusions: Two important cortical events associated with thalamic regulation of the cortex, the slow cortical oscillation (SCO) of sleep and the spike-wave complex of generalized epilepsy, have been found to be localized to ventromedial frontal cortex, specifically to orbital and frontopolar regions. In the present patient’s data, we observed the initial discharges of the generalized seizure to evolve from an SCO localized to orbital and frontopolar cortex. This finding suggests that the frontothalamic control over the sleep mechanism in this patient is involved in the pathophysiology of his seizures.