Abstracts

Rationale: Magnetic Source Imaging is now an accepted noninvasive method of identifying hemispheric language dominance in patients undergoing surgical resection for epilepsy or brain tumor. While a reliable paradigm for localization of memory function has not yet been described, approximately 75% of clinical cases demonstrate some mesial temporal activation during language testing. The current study reports a possible relationship between specific MSI activity sites in the hippocampus or amygdala during an auditory language task, and recognition memory performance on the intracarotid amobarbital procedure (IAP).Methods: The subjects were 24 candidates for resective surgery to treat epilepsy or brain tumor. All patients had undergone the IAP and were classified with left language dominance (n=20) or bilateral language with greater involvement of the left hemisphere (n=4). IAP memory was assessed with a maximum of 16 items and only items presented prior to first motor return were included in the analysis. A passing score was defined as correct recognition of at least 60% of items following full recovery from the drug. The MEG unit consisted of a 148-channel Magnes 2500 WH system (4-D Neuroimaging, San Diego, CA) housed in a magnetically shielded room. Single equivalent current dipole (ECD) model across each whole hemisphere was used in the analysis. MSI language mapping was performed with an auditory word recognition task which has been shown to reliably activate temporal lobe language specific cortex. Activation of the mesial temporal (MT) region was rated as present or absent for each hemisphere based on activity sites specifically within the hippocampus or amygdala. MT activation in relation to IAP memory performance in each hemisphere was compared using Pearson Chi-Square analyses.Results: The presence of MT activation was noted in the left hemisphere of 15 patients (62%), and in the right hemisphere of 9 patients (37%), while 6 patients (25%) showed bilateral MT activation. Seventy-four percent of patients passed the IAP memory test with the left hemisphere, while 46% passed with the right hemisphere. Ten patients (42%) passed the memory test with both hemispheres. Chi-Square analyses comparing MT activation to IAP memory performance was not significant for the left hemisphere, but an association between MT activation and IAP memory was demonstrated for the right hemisphere (p < .01).Conclusions: MSI activation of the mesial temporal lobe in response to an auditory recognition task may be related to IAP memory performance, at least within the nondominant (right) hemisphere. The potential clinical utility of this finding for surgical decision making, including prediction of post operative memory outcome deserves further investigation.