Oscillatory synchronization at low frequencies (<15 Hz) is a powerful mechanism by which neural networks coordinate their activities. Slow oscillations are transmitted with minor phase delay between distant brain regions, and thus provide a flexible signal to synchronize neuronal firing and locally generated fast (high beta, gamma) oscillations in these structures (Buzsaki 2002). In particular, rhythmic synchronization of hippocampus (HC) and prefrontal cortex (PFC) are thought to mediate key cognitive functions, such as working memory (Benchenane et al. 2010; Sauseng et al. 2010; Anderson et al. 2010; Hyman et al. 2005) or goal-directed spatial navigation (Ito et al. 2015). Disruptions in HC-PFC coupling may mediate some of the pathophysiology of schizophrenia (Cousijn et al. 2015; Dickerson et al. 2010; Sigurdsson et al. 2010; Vertes 1981). The overwhelming majority of prior studies emphasized the role of PFC-HC coupling at theta frequency (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). Theta rhythm is the most prominent oscillatory signal in the rodent brain
