PRIMARY OR WORKING-MEMORY IN FRONTAL-LOBE EPILEPSY - AN (18)FDG-PET STUDY OF DYSFUNCTIONAL ZONES

Introduction: We previously demonstrated that patients with frontal lo be epilepsy show deficits on a visual working memory paradigm and that this paradigm produces increased (18)FDG uptake in the dorsolateral p refrontal cortex (DPFC), premotor cortex, angular and supramarginal gy ri, basal forebrain, and ventral frontal poles of normal subjects when compared with a control task. We hypothesized that subjects with fron tal lobe epilepsy would have impaired frontal activation during this t ask. Methods: One resting and two activated images were obtained with (18)FDG-PET in 15 subjects and 14 controls. One was a delayed (DMS) an d one an immediate (IMS) match to sample paradigm. Discriminant and fa ctor analyses were used to analyze the data, supplemented by selected t tests. Results: No differences in glucose uptake were found between the DMS and IMS in the epilepsy subjects, in distinct contrast to cont rols. A comparison between controls and epilepsy subjects showed diffe rences both ipsilateral and contralateral to the epileptic focus in th e frontal regions involved in the task, with small changes in nonfront al, task-related regions as well. The task itself brought out or highl y exaggerated differences seen at rest. There was weak evidence that o ther frontal and temporal regions were attempting to compensate for th e DPFC deficit. Conclusion: A unilateral epileptic focus is capable of suppressing function along a large task-related circuit ipsilateral a nd contralateral to the focus. Peripheral cortical regions compensate poorly for the area of dysfunction.