Prior tracing studies demonstrate the possibility of the midline thalamic nRE as a potential candidate for mediating communication from the PFC to HC (Vertes et al. 2007; Varela et al. 2014). For theta oscillations, we found that controlling for nRE influence via partial correlations had minimal effect on HC-PFC correlation, and lidocaine inactivation also had minimal effect on HC-PFC coherence at theta. These results support prior evidence that HC-to-PFC communication occurs through a monosynaptic connection that is not be influenced by the nRE (Swanson 1981; Ferino et al. 1987; Jay and Witter 1991; Hoover and Vertes 2007). For the 4 Hz oscillation, in contrast, removal of nRE influence through partial correlations significantly affected HC-PFC correlations, and lidocaine inactivation of the nRE significantly reduced 4-Hz coherence. Together, this suggests that the nRE plays an important role in PFC-to-HC synchronization.
