EFFECTS OF TEMPORAL VERSUS TEMPORAL PLUS EXTRA-TEMPORAL LOBE EPILEPSIES ON HIPPOCAMPAL ERPS - PHYSIOPATHOLOGICAL IMPLICATIONS FOR RECOGNITION MEMORY STUDIES IN HUMANS

The present experiment was designed to investigate the incidence of te mporal and extra-temporal epileptogenic lesions on hippocampal activit y related to recognition memory. Hippocampal event-related potentials (ERPs) were recorded during a recognition memory task for pictures in patients with unilateral temporal lobe epilepsy and in patients with c ombined temporal and extra-temporal (frontal or parietal) epileptogeni c foci, In the first group, the comparison between correctly recognize d pictures and new distracters revealed that the usual ERP (N400/P600) 'old/new' effects were not dramatically affected by the presence of a temporal epileptogenic lesion. In contrast, these effects were absent in multifocal epilepsy patients, indicating that frontal and parietal brain regions play a part in the modulation of hippocampal ERP and re lated memory processing. These results suggest that ERP 'old/new' effe cts are dependent on interactions between frontal, parietal and medial temporal structures. Together with the results of other recent studie s devoted to locating the neural sources of N400 and P600, the present findings provide physiopathological evidence that ERP 'old/new' effec ts are subtended by distributed yet interconnected brain regions that are known to play an important role in recognition memory processing.