Rhythmic production of consonant-vowel syllables synchronizes traveling waves in speech-processing brain regions
Nature is abundant in oscillatory activity, with oscillators that have the remarkable ability of synchronizing to external events. Using electrocorticographic (ECoG) recordings from a subject rhythmically producing consonant-vowel syllables (CVSs) we show that neural oscillators recorded at individual ECoG electrodes become precisely synchronized to initiations of the production of CVSs (i.e., that these initiations occur at precise phases of bandpassed-filtered voltages recorded at most ECoG electrodes). This synchronization is not a trivial consequence of the rhythmic production of CVSs, since it takes several minutes to be fully established and is observed at the frequency of CVS production and at its second harmonic. The phase of filtered voltages at which CVSs are produced varies systematically across the grid of electrodes, consistently with the propagation of traveling waves (TWs). Using these synchronized phases we isolate a first TW in voltages (filtered at the median CVS-production frequency) moving from primary auditory to premotor cortex, and a second TW in high-gamma amplitude (coupled to phase at the CVS-production frequency) moving along the same path but in opposite direction. To our knowledge, this is the first report of rhythmic motor acts synchronizing spatio-temporally organized cortical activity in the human brain.