PROPAGATION PATTERNS OF TEMPORAL SPIKES

In standard EEG recordings, spikes appear as single events characterized mainly by the scalp location of the their peak voltage. The signal-to-noise ratio of raw EEG is usually too high to permit more detailed analysis. We used spike averaging to improve the resolution of interictal spikes in 40 patients with temporal lobe epilepsy. Spikes were identified visually in raw, digitally stored EEG. When multiple spike types were present in a patient, they were grouped separately. Spikes were synchronized for averaging by aligning their negative peaks in a designated channel. Sixteen patients demonstrated spike propagation from anterior temporal to posterior temporal electrode locations. Thirty-six patients demonstrated spread of spikes from anterior temporal to fronto-polar electrode sites. While anterior temporal and fronto-polar spikes were often synchronous, fronto-polar spikes followed anterior temporal discharges in 25% of cases and preceded them in 13%. Spike averaging revealed propagation patterns not apparent on visual inspection of raw EEG. We speculate that these patterns may reflect inherent physiological properties of temporal and frontal neuronal circuits, possibly utilized by the epileptogenic process.