Abstracts

Rationale: Evaluation of language activity of the brain is important for planning epilepsy surgery. Magnetoencephalography, a non-invasive neuroimaging procedure, maps verbal function by using language tasks such as semantic decision, picture naming and verb generation. However, some patients cannot perform these tasks due to their limited verbal skills. The purpose of this study is to assess the feasibility of passive auditory language task for evaluating neuronal activity of language. Methods: Four intractable epilepsy patients (male: 3, female: 1, age: 4-16, right-handed: 2, left-handed: 2) were retrospectively studied. MEG was recorded with a 306-channel whole-head system at a sampling rate of 600Hz. In all patients, high-resolution 3T anatomical MRI data were acquired with magnetization-prepared rapid acquisition gradient-echo (MPRAGE). During MEG recording, patients performed a passive word listening task with 160 English words. Interstimulus interval was 3000 ms. MEG data epochs from 500ms pre-stimulus and 1000ms post-stimulus period were averaged after preprocessing. We calculated spatiotemporal source distribution of the averaged data by using dynamic statistical parametric maps (dSPMs). DSPMs were visually mapped on the MRI-derived cortical surface reconstructed by Freesurfer. We also calculated laterality index (LI) by using regions of interest (ROIs) based on the cortical parcellation obtained by Freesurfer. We selected superior temporal, middle temporal, supramarginal, inferior parietal cortices, opecular and triangular parts of the inferior frontal lobe on both hemispheres for ROI analysis, based on a priori knowledge of Wernicke and Broca areas. LI was obtained by LI = (L-R)/(L+R), where L and R is the number of unit dipoles with an F value higher than the threshold in the ROIs within a time window of 250-550ms post stimuli. The threshold was determined as the half of the maximum value over all ROIs. Language laterality was estimated based on the LI as follows; ≥0.1:left, 0.1>LI>-0.1:bilateral, ≤-0.1:right. Results: Primary auditory response was observed at 100ms post stimuli. Possible language activity was observed around 400ms post-stimuli. In right-handed patients, one showed activation in the left posterior temporoparietal and inferior frontal cortex (LI=0.70). The other one showed right temporal activation (LI=-0.63). Two left-handed patients showed right temporoparietal and inferior frontal activation (LI=-0.28, -0.14). Conclusions: The results of our study suggest that the passive auditory word task activates the language function of the brain. MEG recorded during the task performance may provide information for estimating the language laterality in presurgical evaluation.