The strong correlation between nRE at the two rhythms with the structures of their presumed origin, especially remarkable for PFC-nRE (Fig. 4B), suggested that nRE may serve as a relay to establish PFC-HC oscillatory coupling. nRE is reciprocally connected to both PFC and HC which allows for the three structures to synchronize their activities. Thus in the third analysis, we used partial correlation to calculate the residual PFC-HC correlation after allowance was made for the variations in the rhythmic components of the nRE signal. Only significant correlations were partialized, i.e. for this analysis we only used the experiments in which PFC-HC correlations were significant at both 2–5 Hz and theta frequencies (n=7; Fig. 5A–B, note larger PFC-HC and smaller HC-nRE correlations in this group). For 2–5-Hz oscillations we found a significant decrease in PFC-HC correlation when controlling for nRE (student’s paired t-test, p <0.001), from r = 0.81 ± 0.03 to r = 0.13 ± 0.12 (Fig. 5C–E) indicating that nRE contributes to 2–5-Hz synchrony between the PFC-HC, and removal of this influence completely eliminates residual PFC-HC correlation. In contrast,
