The inferences for understanding the dynamical network controlling PFC-HC coupling and the role of nRE, based on prior anatomy and the current findings, are summarized in Fig. 7A. Thus, theta rhythm was the dominant signal in the HC, which correlated with theta power in the PFC. This relationship was minimally affected by the nRE signal. In comparison, the 2–5 Hz oscillation was the dominant frequency in the PFC, and correlated with the power in the HC. This signal was diminished by both statistical and pharmacologic removal of nRE influence. Although correlational analysis does not test directionality, together, these results provide strong evidence that HC-to-PFC communication occurs by synchronization of theta oscillations, whereas PFC-to-HC communication occurs through synchronization of a 4-Hz signal, and this latter is mediated by a synaptic relay in the nRE.
