  Rhythm is a fundamental component of the auditory world, present even during
the prenatal life. While there is evidence that some auditory capacities are
already present before birth, whether and how the premature neural networks
process auditory rhythm is yet not known. We investigated the neural response
of premature neonates at 30-34 weeks gestational age to violations from
rhythmic regularities in an auditory sequence using high-resolution
electroencephalography and event-related potentials. Unpredicted rhythm
violations elicited a fronto-central mismatch response, indicating that the
premature neonates detected the rhythmic regularities. Next, we examined the
cortical effective connectivity underlying the elicited mismatch response using
dynamic causal modeling. We examined the connectivity between cortical sources
using a set of 16 generative models that embedded alternate hypotheses about
the role of the frontal cortex as well as backward fronto-temporal connection.
Our results demonstrated that the processing of rhythm violations was not
limited to the primary auditory areas, and as in the case of adults,
encompassed a hierarchy of temporo-frontal cortical structures. The result also
emphasized the importance of top-down (backward) projections from the frontal
cortex in explaining the mismatch response. Our findings demonstrate a
sophisticated cortical structure underlying predictive rhythm processing at the
onset of the thalamocortical and cortico-cortical circuits, two months before
term.
