Abstracts

Rationale: The Wada procedure is used to assess hemispheric language and memory capacity. In temporal lobe epilepsy (TLE) patients with mesial temporal sclerosis (MTS), poor memory performance is expected with the anesthetic injection contralateral to seizure onset and clear evidence of MTS. However, we have observed a small series of TLE patients with ipsilateral MTS who unexpectedly demonstrate perfect memory performance under these conditions. Methods: Five patients (ages 12, 26, 28, 29, 32; 3 women; 4 right-handed) with refractory epilepsy underwent neuropsychological evaluation, EEG, neuroimaging (MRI and PET) and Wada procedure as part of pre-surgical evaluation. For Wada testing, the left internal carotid artery (ICA) was injected first (to test language and memory within the right hemisphere) with 4 to 6.5 mg of sodium methohexital. The dosage was considered effective upon achievement of unilateral EEG slowing on the side of the injection and contralateral dense hemiplegia. Memory items were presented during this “post-injection period.” Following a 10 minute delay and full recovery, memory was assessed by either spontaneous recall or multiple choice options. Confidence was also assessed on a scale from 1 (guessing) to 3 (very sure) for correct multiple choice items (incorrect items were assigned a score of “0” and spontaneously recalled items were automatically assigned a score of “3”). A total average confidence score = 2.00 was considered “passing.” After approximately 15 minutes, this procedure was repeated with the right ICA injection. Hemispheric language dominance was determined by post-injection aphasia and paraphasic errors upon return to baseline. Radiologists rated angiograms for extent of filling within the anterior, middle, and posterior cerebral arteries and the posterior communicating artery. Results: Neuropsychological evaluations revealed average intellectual functioning (mean FSIQ = 94.6, SD = 12.34) and normal verbal memory on a list-learning test (range = 21%ile to 93%ile) across patients. EEGs demonstrated a pattern of left-sided ictal and interictal abnormality. MRIs showed clear left MTS. PETs determined that there was asymmetric reduced glucose metabolism in the left medial temporal lobe. Wada results were notable for left hemisphere language dominance in all patients. Contrary to expectation, all patients were 100% accurate and had passing confidence (range = 2.2 to 3.0) on memory testing during the right ICA injection. Maximal arterial filling was observed in 4 of 5 patients with one patient exhibiting maximum filling in all arteries except the posterior communicating artery, which had “moderate” filling. Conclusions: Unexpectedly, Wada testing within the above subgroup of patients revealed perfect memory with good confidence on the same side as left MTS. These results potentially carry important implications for surgical TLE patients, raising questions regarding the functionality of sclerotic hippocampi versus the possibility of reorganization of memory to ipsilateral, extra-hippocampal regions. Funding: None.