The second goal of this study was to examine how this PFC oscillation is communicated to HC in this model. Abundant anatomical and electrophysiological evidence demonstrate the existence of a direct unidirectional HC-to-PFC pathway (Ferino et al. 1987; Swanson 1981; Thierry et al. 2000; Jay and Witter 1991; Hoover and Vertes 2007) mediating HC theta drive to PFC (Anderson et al. 2010; Benchenane et al. 2010; O'Neill et al. 2013; Sauseng et al. 2010; Siapas et al. 2005; Jones and Wilson 2005; Hyman et al. 2005). In comparison, communication in the PFC-to-HC direction is less understood, partly because no known direct anatomical connection exists. Recent tracing studies demonstrate however that PFC fibers form synaptic connections with the thalamic nucleus reuniens (nRE) neurons that then project to the HC (Herkenham 1978; Vertes et al. 2007). Thus, the nRE may provide the critical anatomical link between the PFC and HC (Vertes et al. 2015). Thus, we hypothesized that nRE plays a specific role in 2–5 Hz PFC-to-HC synchronization, whereas theta coupling may use the direct HC-to-PFC projection. In this study, we recorded
