Abstracts

RATIONALE: In a previous work, we showed that the antiepileptic effect of subacute electrical stimulation of the hippocampus (SAHCS) may be due, at least in part, to an inhibitory effect on the excitability of the hippocampal neurons i.e. Increased threshold, decreased amplitude and flattened down the recovery cycles of the hippocampal responses evoked by amygdaloid stimulation. Here, we provided further evidence of such an inhibitory effect of SAHCS on the threshold, duration and symptoms accompanying the local afterdischarges (ADs). METHODS: Hippocampal ADs were produced by acute (15-20 sec trains) high frequency (60 Hz), high intensity (600-4200 uA) hippocampal stimulation. RESULTS: It was found that in patients with relative low threshold (600-1200 uA) ADs, prolongued (560 hs or more) SAHCS significantly increased threshold from 800 to 3600 uA, decreased duration from 158 to 20 sec., and completely blocked accompanying symptoms observed before SAHCS. However, with briefer periods of SAHCS (240-460 hs.) hippocampal ADs may show lower thresholds and longer durations but epileptic symptoms (but not auras) were invariably blocked. CONCLUSIONS: Changes in ADs threshold and duration and accompanying symptoms suggest a strong physiological inhibitory effect of SAHCS. Partially supported by CONACYT Mexico, contracts Nums. 348 A930 and 95 785003.