The motor system and the relationships between speech and gesture
Studies of primate premotor cortex, and, in particular, of the so-called “mirror system” suggest a double hand/mouth motor command system that may have evolved initially in the context of ingestion, and later formed a platform for combined manual and vocal communication. In humans, manual gesture, when it accompanies speech, is tightly integrated with speech production. Speech production itself is influenced by executing or observing transitive actions, and manual actions also play an important role in language development in children, from the babbling stage onwards. Behavioural data reported here even show a reciprocal influence between word and symbolic gestures. Studies employing neuroimaging and repetitive Transcranial Magnetic Stimulation (rTMS) techniques suggest that the system governing both speech and gesture is located in Broca’s area.