Human primary motor cortex shows hemispheric specialization for speech

Hemispheric specialization is a prominent characteristic of the human brain. Should the ‘dominant’ hemisphere possess diierential neural organization for language production in the ‘higher order’ cortex, it would be rational to consider that the primary motor cortex may also show similar hemispheric specialization for speech production. In order to test this hypothesis, we investigated the spatial distribution of neural activities associated with phonation (M1p), silent tongue motion (M1t), and vocalization (M1v) within the primary motor cortex, utilizing independent component^ cross correlation^ sequential epoch analysis of high-¢eld functional magnetic resonance imaging time series. While M1t showed no signi¢cant diierences between the two hemispheres, M1p and M1v exhibited signi¢cant hemispheric diierences. The study demonstrated direct evidence that human primary motor cortex possesses clearcut hemispheric specialization similar to that observed for the higher order cortices. NeuroReport 17:1091^1095 � c 2006 Lippincott Williams & Wilkins.