Activation of right insular cortex during imaginary speech articulation

Human speech articulation is a complex process controlled by a form of 'programming' implemented in the brain. Analysis of speech articulation using neuroimaging techniques is difficult, however, because motor noise is time-locked to the articulatory events. The current magnetoencephalography study, in which 12 participants were required to imagine vocalizing a phonogram after a visual cue, was designed to visualize the prearticulatory 'automatic' processes corresponding to the motor initiation. Magnetic activity correlating with the preparation for articulation occurred in the insular cortices at about 160 ms after the visual cue, and had a relative dominance in the right hemisphere. This suggests that motor control of speech proceeds from the insular regions, although the 'automatic' nature of our task might have led to the observed right-sided dominance.