Generation of scalp discharges in temporal lobe epilepsy as suggested by intraoperative electrocorticographic recordings

摘要

OBJECTIVES—To studythe variability, topography, polarity, duration, and incidence ofinterictal epileptiform discharges (EDs) in the scalp EEG andelectrocorticogram (ECoG) from 16 patients with temporal lobe epilepsywho underwent surgical treatment.
METHODS—Preoperativescalp EEGs during quinalbarbitone induced sleep were compared withpreresection ECoGs obtained under general anaesthesia. The analysis wasbased on the initial ECoG record obtained before activation byintravenous thiopentone, and the EEG during stages I and II of sleep.
RESULTS—On the scalp,15 patients had a single discharge pattern, spikes were predominantlynegative, EDs were of largest amplitude at the anterior temporalelectrode in 13 patients and mean discharge incidence was 4.0 (SD 4.2)discharges/min. In ECoG recordings, nine patients had two independentECoG patterns, the polarity of spikes was negative, positive-negative,or positive, the site of maximal amplitude varied greatly betweensubjects, discharge incidence was 7.3 (SD 3.9) discharges/min. Therewas no relation between the topography of the largest spikes on thescalp and in the ECoG. In 14 patients, scalp spikes showedstatistically significant longer duration on the scalp than in theECoG. In seven patients who had frequent widespread ECoG discharges,averaging spikes across ECoG channels generated spiky patterns ofduration similar to that of scalp spikes.
CONCLUSION—It seemsthat, in temporal lobe epilepsy, scalp discharges originate fromwidespread ECoG discharges and tend to produce a stereotyped pattern onthe scalp with largest amplitudes at the anterior temporal electrodes.This is probably due to local anatomical peculiarities in the braincoverings, such as skull discontinuities, rather than to the locationof neuronal generators within the temporal lobe. Due to spatiotemporalaveraging, widespread cortical discharges which become asynchronousduring propagation appear with increased duration and blunted waveformin the EEG, whereas sharply localised phenomena such as positive focalspikes are not recorded from the scalp.