Delayed verbal memory retrieval: A functional MRI study in epileptic patients with structural lesions, of the left medial temporal lobe

In a previous functional magnetic resonance imaging (MRI) study, we suggest ed that in left medial temporal lobe epilepsy (LTLE) poor verbal episodic m emory performances were sustained by abnormal neocortical and mesiotemporal activations. In the present study, we attempted to examine the evolution o f these abnormal neocortical and mesiotemporal activations over 24 h. We th us observed the MRI brain regions activated during the 24-h-delayed retriev al of a word list in the same sample of healthy control subjects and LTLE p atients. In control subjects, a similar left occipitotemporofrontal network was activated during both immediate and 24-h-delayed retrieval conditions. In addition, the 24-h-delayed retrieval also activated a larger parietal r egion and the right hippocampus. This distributed neocortical and mesiotemp oral network was very poorly activated during the 24-h-delayed retrieval in LTLE patients, suggesting the inability to reactivate areas that are keys to retrieving stored information. (C) 2001 Academic Press.