SPW-Rs have been hypothesized to play a critical role in transferring transient memories from the hippocampus to the neocortex for permanent storage (Buzsáki, 1989; McClelland et al., 1995). In line with this postulated role, both place cell sequences and the distances between the place fields experienced during exploration are reflected in the temporal structure of neuronal sequences during SPW-Rs (Figure 7A, B; Kudrimoti et al., 1999; Lee and Wilson, 2002; Nádasdy et al., 1998; O’Neill et al., 2008; Skaggs and McNaughton, 1996; Wilson and McNaughton, 1994) and their selective elimination after learning interferes with memory consolidation (Ego-Stengel and Wilson, 2010; Girardeau et al., 2009). In the waking animal, SPW-R-related sequences can be replayed in either a forward manner, typically prior to initiating a journey, or in a reverse order after reaching the goal (Fig. 7A; Diba and Buzsáki, 2007; Foster and Wilson, 2006). This bidirectional re-enactment of temporal sequences may also contribute to the establishment of higher-order associations in episodic memory.
