We used a Bayesian decoder with a uniform prior to translate the ensemble spiking of these events into probability distributions over position using place fields recorded in a previously experienced environment (Davidson et al., 2009; Karlsson and Frank, 2009) (see Experimental Procedures). In this example, the neurons with place fields near the center well fired at the beginning of the SWR whereas neurons with place fields further from the center well fired progressively

later (Figure 1D; significant replay event; bootstrap resampling p < 10−5). Thus, during this MDV3100 order SWR a previously experienced behavioral trajectory was reactivated. We consistently observed the participation of neurons from spatially distributed networks during SWRs. Across all sessions, 98% (655/667) of significant replay events included neurons from both CA1 and CA3, and 89% (589/667) included neurons KPT-330 from both hemispheres. As reactivation depends on the integrity of the CA3-CA1 network (Nakashiba et al., 2009) and originates within the hippocampus (Chrobak and Buzsáki, 1994, 1996; Sullivan et al., 2011), these results suggest that a spatially coherent network pattern coordinates activity across CA3 and CA1 bilaterally during SWRs. To determine how activity in CA3 and CA1 could be coordinated across hemispheres during SWRs we examined

CA1 SWR triggered spectrograms of the local field potential (LFP) recorded in CA3 and CA1 (Figures 2A and 2B). Spectrograms were computed for 400 ms before and after SWR detection using the multitaper method (Percival and Walden, 1993; Bokil et al., 2010). As multiple SWRs can occur in trains with close temporal proximity (Davidson et al., 2009) we restricted our analysis to the first SWR of each train. Spiking during SWRs differs depending on whether the animal is awake or in a quiescent, sleeplike state (O’Neill et al., 2006; Karlsson and Frank, 2009; Dupret et al., 2010), so we examined awake and quiescent SWRs separately.

aminophylline We found that in addition to the expected increase in ripple power, there was a substantial increase in a 20–50 Hz slow gamma band in both CA3 and CA1. There was also an increase low frequency power (<20 Hz) in CA1, but not in CA3 (Figure S3), likely corresponding to the sharp-wave (Buzsáki, 1986), which reflects CA3 input to CA1. To identify the slow gamma band we band-pass filtered (10–50 Hz) the LFP signal during SWRs and converted the time between the peaks of the resulting signal into an estimate of instantaneous frequency. There was a unimodal distribution in both CA1 and CA3 centered at ∼29 Hz (Figure 2C), indicating that gamma during SWRs is unlikely to be composed of two distinct oscillators.