Quantitative analysis of depth spiking in relation to seizure foci in patients with temporal lobe epilepsy

Abstract

The statistical properties of interictal EEG spiking in medial temporal lobe sites were analyzed in 14 patients with medically refractory complex partial seizures in whom the anatomical origins of seizure episodes had been inferred through the assessment of electrographic seizure records. An automatic spike recognition system programmed for a minicomputer was optimized and used to quantify spike abnormalities. The relationship of spike properties across recording sites within patients was found to exhibit stability across a period of days. Within each patient, the temporal lobe which appeared to be most likely to initiate electrographic seizure episodes was found to contain a site or sites exhibiting the maximum mean spike rate, the minimum standard deviation of interspike intervals, and the minimum coefficient of variation in spiking. Certain values of these measures of spiking may be indicative of a strong likelihood of eventual seizure initiation from the region being monitored. The degree of lateralization of depth spike activity was found to correlate perfectly with the suitability of patients from unilateral temporal lobectomy as judged by electrographic seizure recordings. While the relation between depth spike occurrence and the apparent origin of seizure episodes was found to be a very close one, a relation between depth spike occurrence and time of seizure onset was usually not evident. These data indicate the usefulness of interictal depth spike activity in predicting the electrographic locus of depth originating seizure episodes as well as the potential usefulness of such information in forming a surgical prognosis.