Abstracts

RATIONALE:_Clinical and pathological evidence suggests that bilateral hippocampal involvement, whether obvious or subtle, is present in some degree in most patients with medial temporal lobe epilepsy (MTLE). In this study, we questioned whether impairment of verbal memory that is usually associated with left-sided MTLE (LTLE) could also be present in right-sided MTLE (RTLE), raising out the possibility of a bilateral hippocampal dysfunction. In patients engaged in verbal memory tasks, we sought to evidence widespread patterns of activations that could be the witness of this bilateral hippocampal dysfunction. METHODS:_BOLD fMRI data were collected from 14 patients (7 left-sided and 7 right-sided hippocampal sclerosis) and 10 control subjects on a 3T Brucker. 22 contiguous images covering the whole brain were acquired using an EPI echoplanar sequence. Subjects were instructed to learn a list of 17 words, and to recall it immediately and at 24 hours interval. Group analyses were performed using SPM96. RESULTS:_RTLE patients retrieval performances were significantly impaired as compared to the performance of control subjects but were better than those of LTLE patients. All patients exhibited consistent and extensive prefrontal activations in all the memory tasks as compared to the controls subjects. Activation of the hippocampus was only detected in control subjects in the right side, during the 24h delayed recalls (two foci: x=27, y=-36, z=0 mm and 24, 39, 3; p<0.0001). Neither left or right MTLE patients exhibited hippocampal activation during the verbal memory tasks. CONCLUSIONS:_MTLE cannot be considered as a model of pure hippocampal dysfunction. The verbal memory impairment depicted in RTLE patients may be attributable to the propagation of the epileptic discharges into contralateral temporal regions. This impairment seems correlated to widespread extratemporal brain activations.