Correlates of human handedness in primary motor cortex: a review and hypothesis.

A review of the research on anatomical and functional asymmetries in human primary motor cortex suggests that the area of hand representation is greater in the dominant than in the non-dominant hemisphere and that there is a greater dispersion of elementary movement representations with more profuse horizontal connections between them. The more profuse interconnections in motor cortex (M1) of the dominant hemisphere might form a neural substrate which favors the formation of experience-dependent excitatory and inhibitory interactions between elementary movement representations. Motor practice might lead to more precise spatiotemporal coordination of the activity of the elementary movement representations in M1 of the dominant than that of the non-dominant hemisphere, thus leading to more dexterous behavior of the dominant than that of the non-dominant hand.