Frontal/Medial Temporal Lobe Contributions to Memory

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DESCRIPTION (provided by applicant): Neuroimaging studies have suggested involvement of both frontal and medial temporal regions during memory formation. The evaluation of medial temporal lobe function is necessary prior to temporal lobectomy for epilepsy to avoid postoperative amnesia. Injection of the anesthetic, amytal, into the internal carotid artery has been used to predict whether the side opposite surgery can sustain memory. The resulting memory impairment is poorly predictive of postoperative memory decline. Frontal lobe activation in memory could explain these results given the limited perfusion of medial temporal lobe structures with amytal injections. Further, similar lateralizing effects of the type of material memorized have been described for both frontal lobe activation and cerebral amytal results. In the proposed studies, functional MRI (fMRI) of memory encoding would be performed in patients undergoing cerebral amytal testing and subsequent temporal lobectomy. These fMRI studies are proposed to: 1) Image medial temporal lobe (MTL) functional activity in patients who are candidates for temporal lobectomy to treat seizures. Activation of both left and right MTL will be optimized using different encoding paradigms. 2) Demonstrate superior predictive value of postoperative memory performance with fMRI of memory compared to the predictive value of the cerebral amytal test. Preoperative fMRI studies will attempt to demonstrate both the integrity of the MTL opposite the side of operation as well as any remaining function on the side of surgery. 3) Demonstrate better correlation with frontal lobe activations than MTL activations with results of the cerebral amytaL consistent with the known distribution of intracarotid injections. 4) Follow the plasticity of frontal lobe activations following temporal lobectomy. Functional MRI of postoperative patients, who undergo temporal lobectomy, will be performed to determine if frontal lobe activation during memory encoding remains, and if it retains its preoperative lateralization with encoding different material. This final aim will help establish the relationship between ipsilateral frontal and medial temporal lobe activation.