Abstracts

Rationale: Head-surface EEG can be configured to display voltage gradient change in a computer-generated cartoon image sequence. FIET peak movement in space domain is easily appreciated and suggests propagation within the epileptogenic neuron matrix. Such a review-analysis is too impressionistic to generate a useful summary of FIET geometry. A simple protocol to capture spatiotemporal data from time-domain peaks in polygraphic EEG, and plot them in a series of head-surface maps, was applied to a randomly chosen set of FIET in this exploratory study. Methods: One representative FIET was chosen from each of 110 consecutive EEG records in a 2-year period. A total of 23 head-surface electrodes included the 10-20 System and 2 basal pairs (zygomatic and mastoid). FIET, less than 150 ms in duration, were ranked by conventional waveform criteria. The top 50 FIET were examined in common average derivations at highest time resolution. The operator would follow polygraphic channels, manually advancing cursor at 5-ms interval (t), and plot the FIET peak (at most one per channel) onto a STMap panel (18 head-surface maps, designed as modified stereographic projection), covering a period of 90 ms, time-coded from -12t through 5t with 0t set at the dominant peak. STMaps were classified according to the pattern of peak movement. Results: The primary finding was that the longer interpeak latency, the more distant, space domain separation of component peaks. FIET formed 2 contrasting groups, one, 40 FIET with local peak components only, and the second, 10 FIET, with distant as well as local peak components. Local peak components revealed no movement (defined as no peak separation longer than 10 ms) in 17 of 40 FIET in the first group. FIET with distant peak components revealed multiple clustering and latency variation, suggestive of interlobar and/or interhemispheric propagation. FIET duration did not differ significantly between 2 groups. Conclusions: Local peak components are what the clinical electroencephalographer recognizes to infer a localized epileptogenic matrix, conventionally represented by the dominant peak, while FIET peak movement to distant locations is suggestive of secondary epileptogenesis, and refractoriness to treatment. The significance of peak movement near the dominant peak, seen in 23 FIET, is to be further investigated. The dominant FIET peak more often belonged to the basal hemisphere, reflecting a larger number of FIET of presumed temporal lobe origin. Geometric examination of FIET peak components may help better define the clinical neurophysiology of epileptogenesis, and its natural history.