Limbic event-related potentials to words and pictures in the presurgical evaluation of temporal lobe epilepsy

SummaryWe recorded limbic event-related potentials (ERPs) with intrahippocampal depth electrodes in a more demanding verbal and an easier pictorial continuous recognition task in patients undergoing presurgical evaluations of their medical refractory mesial temporal lobe epilepsies (MTLE). In all cases depth electrodes were implanted because non-invasive studies could not demonstrate unilateral seizure-onset unequivocally. For the present study we only considered 24 patients who eventually were found to suffer from unilateral MTLE, in whom hippocampal sclerosis (HS) was confirmed histologically, and who were seizure-free post-operatively. We found that the rhinal anterior medial temporal lobe N400 (AMTL-N400) to first presentations of words but not to pictures was reduced in amplitude on the side of seizure origin. Our data suggest that limbic ERPs to words are more sensitive to the epileptogenic process than those to pictures. Thus, if limbic ERPs are recorded as part of invasive presurgical evaluations, verbal instead of pictorial recognition paradigms should be employed.