  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.

Neurons and Cognition