The role of hippocampal-PFC gamma interactions in memory processes is still not clear and requires further elaboration. How the distinctive place cell sequences seen during slow and fast gamma rhythms in CA1 [70] relate to activity beyond the hippocampus remains unknown. The finding that hippocampal gamma rhythms are modulated by theta oscillations [32,57], and PFC gamma is influenced by hippocampal theta [29], suggests the existence of a fine temporal relationship between hippocampal and prefrontal gamma activity. In addition, the fact that hippocampal SWR replay is correlated with periods of slow gamma coherence [58–60] raises the possibility that coordinated reactivation of behaviorally relevant information in hippocampal-prefrontal networks may be influenced by gamma. It has also been recently shown that inactivating direct ventral hippocampal inputs to PFC during memory-guided behavior impairs gamma oscillations and task representations in PFC, and selectively affects memory encoding [30]. Hence, current evidence suggests a functionally important coordination of gamma rhythms between the two regions, which requires further investigation.
