Abstracts

Rationale: Localizing language receptive (i.e., Wernicke s) area and expressive (i.e.,Broca s) area are crucial for pre-surgical planning in patients with epilepsy and brain tumors, using non-invasive functional imaging techniques, such as Magnetoencephalography (MEG). It has been reported that \ Wernicke s area can be reliably localized using MEG [1]. However, it has been challenging to localize both Wernicke and Broca s areas using one language test with MEG. In the present study, we investigate a new approach of localizing both language receptive and expressive areas with one procedure using MEG. Methods: Fourteen healthy control subjects and four pre-surgical patients were examined using a new MEG language test. In this approach, language mapping of receptive and expressive language-specific areas was assessed using a word recognition and silent reading task. In this task, four tumor patients were asked to listen toand remember target words first, then recognize and silently read the target words from a mix of the target words and new words. A whole-head MEG system (Elekta/Neuromag VectorView) with 306 channels was used to record the language responses. The MEG data was first run through MaxFilter [2][3] to remove external interferences (e.g., magnetic artifacts due to metal objects, strong cardiac signals, environment noises, etc.), and to correct for head movement. The artifact-free MEG signals were averaged with respect to the onset of the stimuli. The trial-averaged MEG responses were then analyzed using the equivalent-current-dipole (ECD) model in the Elekta/Neuromag software package. Results: In healthy control subjects and pre-surgical patients, we were able to localize the primary language areas, including Broca s area in the left inferior frontal cortex (Brodmann areas 44 and 45) and Wernicke s area in the posterior aspect of the left superior temporal gyrus. The top row of Fig. 1 shows the language-receptive area in the left hemisphere localized by MEG using the new approach, and the bottom row is for the language expressive area obtained during the same task. Similar result is shown in Fig. 2 for another pre-surgical patient with a right hemisphere lesion. Conclusions: MEG is a non-invasive functional imaging technique which can localizelanguage-specific areas. Our results show that the word-recognition/ silent reading task can identify the language dominant hemisphere and localize the expressive speech area as well as the receptive-language area in pre-surgical patients. [1] Papanicolaou AC, Simos PG, Castillo EM, Breier JI, Sarkari S, Pataraia E, Billingsley RL, Buchanan S, Wheless J, Maggio V, and Maggio WW. Magnetocephalography: a noninvasive alternative to the Wada procedure. J.Neurosurg. 100: 867-876, 2004. [2] Taulu S, Simola J, and Kajola M. MEG recordings of DC fields using the signal space separation method (SSS). Neurol.Clin.Neurophysiol. 2004: 35, 2004. [3] Song T, Gaa K, Cui L, Feffer L, Lee RR, and Huang M. Evaluation of signal space separation via simulation. Med.Biol.Eng Comput. [Epub ahead of print] PMID: 18196307: 2008.