Abstracts

Rationale: Previously, we demonstrated possible relationships between Magnetic Source Imaging (MSI) mesial temporal (MT) activation using a word recognition paradigm, unilateral memory scores on the Wada test, and the presence of MT sclerosis. Greater activation of the right MT structures was more common in patients with left MTS and corresponded to relatively higher Wada memory scores following left injection. The question of whether MT activation represents memory processing per se vs. other types of cognitive functioning remains unresolved. In the present study, we re-examine MSI MT activation in relation to baseline neuropsychological test scores. Methods: The subjects were 12 epilepsy or brain tumor surgery candidates who had undergone neuropsychological testing and who demonstrated MT activation in response to an auditory word recognition task during receptive language mapping with MSI. All patients had been classified left language dominant based on MSI criteria. The MEG unit consisted of a 148-channel Magnes 2500 WH system and data were analyzed using the single equivalent current dipole (ECD) model across each whole hemisphere. Patients were divided into left and right groups based on the hemisphere with the most MT activation. The two groups were compared on the following measures: Full Scale IQ, Boston Naming Test, Controlled Oral Word Association Test (COWAT), Animal Naming and the delayed recall score on the Verbal Selective Reminding Test (VSRT). The results were compared using the nonparametric Wilcoxen Mann-Whitney U sum of ranks test for small samples. Results: Patients with more mesial temporal activation in the left hemisphere scored significantly higher on Full Scale IQ (mean = 107.4) and confrontation naming on the Boston Naming test (mean = 52) compared to patients with more activation in the right mesial temporal lobe (FSIQ = 92.7; BNT mean = 34.7). A similar trend was noted for the phonemic verbal fluency (COWAT) task but differences were not statistically significant. There was no difference between the two groups on the Animal Naming measure or delayed recall on the VSRT. Conclusions: These limited results lend support to a cognitive interpretation of this MT activity that may extend beyond verbal memory. While performance on a delayed word recall task does not correspond to MT activation ipsilateral or contralateral to the language dominant hemisphere, a possible relationship to other word retrieval scores such as confrontation naming and phonemic verbal fluency is suggested. The explanation of increased MT activation in the right hemisphere of patients with clearly established left hemisphere dominance for language remains undetermined. However, these observations do suggest the need to examine in greater detail the inter-relationship of naming and verbal memory.