Spontaneous endogenous generators are key elements in immature systems. Theta activity (TA) and the coalescent slow waves (SW) occur from 25wGA and address the basic mechanisms of cross frequency interdependencies in oscillations that compose brain rhythms in premature.

To evaluate the interactions between the two oscillations using phase-amplitude coupling.

EEGs of 34 prematures (25–27wGA) were analyzed. Temporal relationships between TA and SW were assessed, using event-locked analysis. SW and TA were automatically detected. Artifact-free epochs time locked to the SW trough were extracted. Time-frequency representations (TFRs) were calculated. To quantify locking between the SW phase and the TA power, a synchronization index was computed. To investigate the temporal relationships between SW and TA, event histograms were created referenced to the SW trough and TA peak.

TFR analysis demonstrated that TA power was increased during the SW descending slope and around the SW trough and showed a lasting suppression during the SW peak. Event histogram analysis confirmed the consistent timing of TA during SW cycle. Maximum TA was reached before the SW trough.

This cross frequency coupling with a so precise intimate temporal relationship between rapid and slow oscillators constitutes an index of “ideal” mechanisms with unique functional and structural wiring in the auditory network, disruptions of which might be of dramatic neurodevelopmental consequences. Coupling between the phase of the slow oscillations and the amplitude of theta oscillations in this early neural biomarker might suggest developing network level dynamics in early prematurity.