Spatially filtered magnetoencephalographic analysis of cortical oscillatory changes in basic brain rhythms during the Japanese 'Shiritori' Word Generation Task

BACKGROUND: 'Shiritori' (capping verses) is a traditional Japanese word generation game, and is very familiar to native Japanese speakers. The shiritori task is expected to more strongly activate temporal language-related regions than conventional word generation to letters because of its characteristic way to make cue letters. OBJECTIVES: The aim of this study was to examine the cortical oscillatory changes in basic brain rhythms during silently performing a shiritori task. METHODS: Using synthetic aperture magnetometry (SAM) analysis of magnetoencephalography, we estimated the tomographic distributions of the statistically significant differences of the power in the alpha and beta frequency bands between the resting and the task periods. RESULTS: Significant event-related desynchronization (ERD) in the 8- to 25-Hz band, thought to reflect neural activation, was localized within task-related cortical regions with left-side dominance. The significant ERDs were estimated in both the frontal and temporal language-related regions encompassing Broca's and Wernicke's areas, although previous neuroimaging studies using word generation to letters showed neural activation predominantly in frontal regions. CONCLUSIONS: Our results show the potential of SAM analysis for reliable brain mapping of language processing, and suggest that the shiritori task might be more suitable for examining the language-related network in the brain than conventional word generation to letters.