  Rhythm processing involves building expectations according to the
hierarchical temporal structure of auditory events. Although rhythm processing
has been addressed in the context of predictive coding, the properties of the
oscillatory response in different cortical areas is still not clear. We
explored the oscillatory properties of the neural response to rhythmic
incongruence and explored the cross-frequency coupling between multiple
frequencies to provide links between the concepts of predictive coding and
rhythm perception. We designed an experiment to investigate the neural response
to rhythmic deviations in which the tone either arrived earlier than expected
or the tone in the same metrical position was omitted. These two manipulations
modulate the rhythmic structure differently, with the former creating a larger
violation of the general structure of the musical stimulus than the latter.
Both deviations resulted in an MMN response, whereas only the rhythmic deviant
resulted in a subsequent P3a. Rhythmic deviants due to the early occurrence of
a tone, but not omission deviants, elicited a late high gamma response (60-80
Hz) at the end of the P3a over the left frontal region, which, interestingly,
correlated with the P3a amplitude over the same region and was also nested in
theta oscillations. The timing of the elicited high-frequency gamma
oscillations related to rhythmic deviation suggests that it might be related to
the update of the predictive neural model, corresponding to the temporal
structure of the events in higher-level cortical areas.
