Routine pre-operative EEG studies as well as direct brain recording and stimulation carried out during operations were analysed for 59 patients subjected to a standard unilateral anterior temporal lobectomy for the treatment of epilepsy. All patients in the present series were 16 years old or older at the time of operation, which was invariably carried out under local scalp analgesia only. Electrophysiological findings was correlated with pathological changes noted in the resected temporal lobes, and with the effects of surgery upon seizure activity. Pre-operative EEG data correlated with each of four pathological categories when sphenoidal electrodes and intravenous barbiturate narcosis were emplyed. Thirty of 31 patients with mesial temporal sclerosis demonstrated medial temporal primary spike foci, frequently with independent contralateral and extratemporal secondary foci. In addition, one-third of these patients demonstrated unilateral focal decreased barbiturate-induced fast activity in the corresponding sphenoidal to ear channels. Twelve patients with other specific medial focal lesions (mostly hamartomas) also had medial temporal primary foci, often with independent contralateral secondaries but never with extratemporal foci. Two patients in this group also demonstrated focal decreased fast activity in the appropriate sphenoidal-ear channel. Both of these groups did very well post-operatively with respect to their epilepsy. Five patients with large temporal convexity cicatrices antedating seizures all demonstrated lateral temporal primary spike foci without independent secondary foci or focal decreased fast activity and did not do as well post-operatively as the first two groups. Eleven patients had only non-specific changes in the resected temporal lobe and in general did not benefit from surgery. Various combinations of primary and independent secondary spike foci were seen. Only this group demonstrated diffuse or bifrontal spikes during initial EEG recording, and basal mid-line spikes with intravenous thiopentone. Pecilar sharp notched spike were also very common in this group, but not unique to it. Focal decreases in barbiturate-induced fast activity were not noted.

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