  We hypothesized that rhythmic motor acts entrain neural oscillations in
speech production brain regions. We tested this hypothesis in an experiment
where a subject produced consonant-vowel (CV) syllables in a rhythmic fashion,
while we performed ECoG recordings. Over the ventral sensorimotor cortex (vSMC)
we detected significant concentration of phase across trials at the specific
frequency of speech production. We also observed amplitude modulations. In
addition we found significant coupling between the phase of brain oscillations
at the frequency of speech production and their amplitude in the high-gamma
range (i.e., phase-amplitude coupling, PAC). Furthermore, we saw that brain
oscillations at the frequency of speech production organized as traveling waves
(TWs), synchronized to the rhythm of speech production. It has been
hypothesized that PAC is a mechanism to allow low-frequency oscillations to
synchronize with high-frequency neural activity so that spiking occurs at
behaviorally relevant times. If this hypothesis is true, when PAC coexists with
TWs, we expect a specific organization of PAC curves. We observed this
organization experimentally and verified that the peaks of high-gamma
oscillations, and therefore spiking, occur at the same times across electrodes.
Importantly, we observed that these spiking times were synchronized with the
rhythm of speech production. To our knowledge, this is the first report of
motor actions organizing (a) the phase coherence of low-frequency brain
oscillations, (b) the coupling between the phase of these oscillations and the
amplitude of high-frequency oscillations, and (c) TW. It is also the first
demonstration that TWs induce an organization of PAC so that spiking across
spatial locations is synchronized to behaviorally relevant times.
