Abstracts

Rationale: Activation within the mesial temporal lobe is often noted in response to a word recognition procedure used for language mapping in a Magnetic Source Imaging (MSI) paradigm. We have previously reported an association between this activation and the integrity of memory processing in the same hemisphere based on unilateral Wada memory performance. Reduced mesial temporal activation has also been reported in epilepsy patients diagnosed with left mesial temporal sclerosis, supporting the likelihood that these activity sites represent memory processing. The current study extends these findings and supports continued use of this paradigm in considering overall cognitive risk associated with mesial temporal resection. Methods: The subjects were 63 adult epilepsy or brain tumor surgery candidates who underwent both MSI language mapping and the Wada test. The MEG unit consisted of a 148-channel magnes 2500 WH system and data were analyzed using the single equivalent dipole (ECD) model across each whole hemisphere. The activation test was an auditory word recognition task in which subjects identified target words repeated on successive trials. The hemisphere with the most MT activity sites (defined as dipoles within a one cm radius of the hippocampus) was identified for each patient. Wada memory scores were assessed with a maximum of 16 items presented prior to the first motor return and calculated as a percent correct for each hemisphere. Results: Seventy-one percent of all patients tested (45 cases) demonstrated some degree of mesial temporal activation. The remaining cases were eliminated from further analyses. Among patients with greater left mesial temporal activation (LMTA), Wada memory scores were significantly higher in the left hemisphere (73% correct) compared to the right (52% correct; t-test for independent samples p < .01). For patients found to have greater right mesial temporal activation (RMTA), Wada memory scores tended to be higher in the right hemisphere (mean 63.5% correct) compared to the left (mean 48% correct), however this comparison did not reach statistical significance (p=.06). MRI data documenting the presence or absence of mesial temporal sclerosis (MTS) were available for 30 patients. Of these, 12 had evidence of left MTS (LMTS) and 83% of the LMTS patients (10/12) also fell in the RMTA group. LMTS patients demonstrated significantly higher Wada memory scores in the right hemisphere (78% correct) compared to the left (43% correct; t-test p < .01). Conclusions: These data further validate the relationship between MSI mesial temporal activation during repetitive word recognition and the memory performance of a single hemisphere during the Wada test. While LMTA appears to correlate with the expected left hemisphere advantage on Wada memory testing, RMTA may identify patients in whom some reorganization of memory to the right hemisphere has occurred, especially in cases of LMTS. Relationship of these findings to language dominance and neuropsychological test results will be discussed. Funding: None