PROPAGATION PATTERNS OF TEMPORAL SPIKES

In standard EEG recordings, spikes appear as single events characteriz ed 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 interic tal spikes in 40 patients with temporal lobe epilepsy. Spikes were ide ntified visually in raw, digitally stored EEG. When multiple spike typ es were present in a patient, they were grouped separately. Spikes wer e synchronized for averaging by aligning their negative peaks in a des ignated channel. Sixteen patients demonstrated spike propagation from anterior temporal to posterior temporal electrode locations. Thirty-si x patients demonstrated spread of spikes from anterior temporal to fro nto-polar electrode sites. While anterior temporal and fronto-polar sp ikes were often synchronous, fronto-polar spikes followed anterior tem poral discharges in 25% of cases and preceded them in 13%. Spike avera ging revealed propagation patterns not apparent on visual inspection o f raw EEG. We speculate that these patterns may reflect inherent physi ological properties of temporal and frontal neuronal circuits, possibl y utilized by the epileptogenic process.