Cortical speech processing mechanisms while vocalizing visually presented languages.

To elucidate cortical processing during vocalization, we used positron emission tomography to measure regional cerebral blood flow during vocalization in six Japanese subjects. During reading Japanese sentences used daily or short syllables aloud, the visual cortices, the left Heschl's gyrus, Broca's area, the primary motor area of the articulatory organs, the supplementary motor area and the cerebellum were significantly activated, compared with resting conditions. The superior temporal gyri were rarely activated. Significant activation of the cerebellum was observed by comparing cortical activity during reading sentences used daily with that during reading meaningless short syllables. These results suggest that vocalization of familiar materials is taken over by the cerebellum, rather than cortical speech areas, and without engagement of the superior temporal gyri.