Abstracts

Rationale: Activation of the mesial temporal region is frequently observed in response to a Magnetic Source Imaging (MSI) auditory language paradigm involving recognition of abstract nouns that are repeated over trials. We have previously reported that this activation may be associated with Wada memory scores, atypical language classification and may be more likely in the right hemisphere of patients with left MTS. The current study examines mesial temporal activation (MTA) in relation to word recognition over trials and 30 minute delayed recall of the same target word list. Methods: The subjects were 29 epilepsy or brain tumor surgery candidates ranging in age from 16 to 66 years who underwent MSI language mapping. 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 were instructed to raise the right (or left) index finger whenever they heard a word from the original target list. Responses were scored for accuracy via video camera for six presentation trials. Delayed recall of target items was elicited 30 minutes following completion of the language task. The presence or absence of MTA was recorded for each subject during the language analysis. Results: Sixteen of 29 subjects (55%) demonstrated MTA during the receptive language task, typically in the language dominant hemisphere. The incidence of MTA was significantly higher (78%) for patients whose trial one recognition score was less than 20 (out of 30) compared to those with higher recognition scores (MTA incidence of 33%; Fisher exact test p=.038). A similar trend was noted for 30-minute delayed recall scores and for "best trial" scores, although these difference did not reach statistical significance. Conclusions: These results suggest an inverse relationship between MTA in the language dominant hemisphere and accuracy of verbal memory processing. The possibility that MSI activation (at least within the mesial temporal region) may represent underlying impairment rather than efficient functioning should be considered.