Functional lateralization of speech production at primary motor cortex

To evaluate lateralization of speech production at the level of the Rolandic cortex, functional magnetic resonance imaging (1.5 Tesla, 27 parallel axial slices, EPI-technique) was performed during a speech task (continuous silent recitation of the names of the months of the year). As control conditions, non-speech tongue movements and silent singing of a well-known melody with the syllable 'la' as its carrier were considered. Tongue movements produced symmetrical activation at the lower primary motor cortex. During automatic speech a strong functional lateralization to the left hemisphere emerged within the same area. In contrast, singing yielded a predominant right-sided activation of the Rolandic region. Functional lateralization of speech production therefore seems to include the precentral gyrus as well as Broca's area.