Abstracts

While fMRI paradigms have been developed for lateralizing and localizing language function non-invasively, memory paradigms have not been well established. We employed an fMRI paradigm to specifically activate the hippocampus (HC) in a consecutive series of intractable temporal lobe epilepsy (TLE) and extratemporal epilepsy (ETE) patients and compared stimulation localization and intensity with other clinical information to assess the validity of this fMRI HC activation. Eleven intractable epilepsy surgical candidates (M:4; F:7, age 16-59 years) were enrolled. Nine patients had TLE (6 unilateral; 3 bilateral) and 2 patients had frontal lobe epilepsy (FLE). All patients had a pre-surgical neuropsychological battery, to include several standardized memory measures. The fMRI memory protocol was performed in a 3-T GE scanner, consisting of a block design with one learning trial and 5 identical recall trials. The learning trial included individual presentation of 10 objects for 3 seconds each, for a total of 30 seconds of memory acquisition. The recall trials included serial presentation of 10 objects for 3 seconds each, 1 or 2 of which were from the original list. The patient pushed one switch to indicate recognition of the object and another switch for absence of recognition. Each epoch was followed by a 30 second rest period; activation maps were generated from a comparison of the 5 recall epochs with the 5 rest epochs. The level of hippocampal activation was identified as normal, reduced, or absent for each side. Visual and verbal memory functions were classified as normal, mildly impaired, or severely impaired. The hippocampal activation pattern was compared with the level of memory impairment. Six of the 9 TLE patients had decreased HC activation ipsilateral to the seizure focus or decreased HC activation bilaterally. Cognitive testing was concordant in these patients, with either severely impaired unilateral memory dysfunction or global memory impairment in the predicted direction. In the 3 bilateral TLE patients, the fMRI revealed decreased HC activation bilaterally; cognitive testing revealed severe verbal and visual memory dysfunction. In 1 FLE patient, mildly decreased HC activation corresponded with mildly decreased verbal and visual memory; the other FLE patient demonstrated significantly decreased HC activation and severely impaired verbal and visual memory. This study indicates this new fMRI memory paradigm is adequately activating the HC and the level of activation corresponds to the seizure focus and pattern of memory impairment. It also reveals localizing information that may be useful in the presurgical evaluation of intractable epilepsy.