Lidocaine was microinfused into the nRE to pharmacologically inhibit its potential contribution to PFC-HC oscillatory coupling. In these experiments, HC field potentials were recorded both in dHC and vHC (2 electrodes in each site), which allowed comparisons based on a total of 8 pairwise combinations of PFC-HC recordings in each rat. Peak coherence values were identified in the delta and theta ranges at RPO stimulus intensities optimal to generate the largest spectral peaks of the two oscillations and compared before and after local lidocaine administration (Fig. 6A, note shift in theta peak frequency from 7.2 ± 0.1 to 5.9 ± 0.2, p=0.02). Lidocaine had little effect on coherence for the theta oscillation (coherence pre-lidocaine = 0.52 ± 0.04, post-lidocaine = 0.48 ± 0.04, p = 0.19, n=32) although it decreased peak theta frequency (7.2 ± 0.1 to 5.9 ± 0.2, p=0.02), suggesting that the nRE does not participate in propagation of theta oscillations between HC and PFC. In contrast, PFC-HC coherence of 2–5 Hz oscillation significantly decreased after lidocaine by 0.39 ± 0.04 (Fig. 6C) from 0.73 ± 0.03 control
